Sensor array-based system and method for rapid materials characterization

ABSTRACT

A modular materials characterization apparatus includes a sensor array disposed on a substrate, with a standardized array and contact pad format; electronic test and measurement apparatus for sending electrical signals to and receiving electrical signals from the sensor array; an apparatus for making electrical contact to the sensors in the standardized array format; an apparatus for routing signals between one or more selected sensors and the electronic test and measurement apparatus and a computer including a computer readable having a computer program recorded therein for controlling the operator of the apparatus. The sensor array is preferably arranged in a standardized format used in combinatorial chemistry applications for rapid deposition of sample materials on the sensor array. The interconnection apparatus and sensor array and contact pad allow measurement of many different material properties by using substrates carrying different sensor types, with only minor modifications if any to the electronic test and measurement apparatus and test procedures. By using a sensor array that is separate from the electronic apparatus, and by including standardized contacting and signal routing apparatuses, the apparatus creates a modular “plug-and-play” system that eliminates the need for multiple materials characterization machines, and eliminates the need for application-specific active circuitry within the sensor arrays themselves. Further, the modular sensor array system can characterize large numbers of material samples rapidly, on the order of at least 50 samples per hour, reducing the time needed for screening of materials libraries.

RELATED CASES

The present application is a continuation-in-part of co-pending U.S.patent. application Ser. Nos. 09/210,086; 09/210,428 and 09/210,485, allfiled on Dec. 11, 1998, and are incorporated herein by reference. Thepresent application is also related to a PCT application having the sametitle and filed concurrently herewith on Dec. 10, 1999.

TECHNICAL FIELD

The present invention is directed to a computer controlled apparatus forcharacterizing a plurality of organic or inorganic materials, and moreparticularly to a characterization apparatus that uses anelectrically-driven sensor array to characterize a plurality ofmaterials simultaneously and rapidly.

BACKGROUND

Companies are turning to combinatorial materials science techniques fordeveloping new compounds or materials (including formulations, materialshaving different processing histories, or mixtures of compounds) havingnovel physical and chemical properties. Combinatorial materials sciencerefers generally to methods and apparatuses for creating a collection ofchemically diverse compounds or materials and to methods and apparatusesfor rapidly testing or screening such compounds or materials for desiredperformance characteristics and/or properties. The collections ofchemical compounds or materials are commonly called “libraries”. SeeU.S. Pat. No. 5,776,359, herein incorporated by reference, for a generaldiscussion of combinatorial methodologies.

A virtually infinite number of useful materials or compounds can beprepared by combining different elements of the Periodic Table ofElements in varying ratios, by creating compounds with differentarrangements of elements, and by creating materials comprising mixturesof compounds or formulations with differing processing histories.Discovery of useful materials for a particular application may requirepreparation or characterization of many candidate materials orcompounds. Preparing and screening a large number of candidatesincreases the probability of useful discoveries. Thus, any system thatcan analyze and characterize the properties of combinatorially preparedlibrary members quickly and accurately is highly desirable.

Many conventional measurement systems comprise a distinct specializedmachine for characterizing a particular material property, so thattesting of a candidate material can use many machines and can becumbersome and time-consuming. Also, most known materialscharacterization devices measure only one material sample at a time,severely limiting the number of samples that can be characterized perunit time.

Optical screening methods and devices have been preferred for manycombinatorial chemistry and combinatorial materials science applicationsbecause they are non-contact and non-destructive. See for example WO98/15805, incorporated herein by reference. For example, luminescencemay be screened optically. When monitoring chemical reactions, forexample, thermal imaging with an infrared camera can detect heatreleased during relatively fast exothermic reactions. See WO 98/15813,incorporated herein by reference. Although optical methods areparticularly useful for characterizing materials or properties incertain circumstances, many materials characterization techniques aredifficult or impossible to perform using optical methods. Therefore,there is still a need for a more direct materials characterizationmethod that involves more intimate contact between the material samplesand the sensing apparatus.

Conventional sensors that generate electrical data corresponding tomaterial properties are typically designed as individual, discreteunits, each sensor having its own packaging and wiring connections. Manymaterials characterization sensors are designed to be used individuallyin or with a machine that characterizes one sample at a time. Linking aplurality of these individual sensors in an array format, assuming thatit is physically possible, would be expensive and often creates overlycomplicated wiring schemes with minimal gains in operating efficiencyfor the overall sensing system.

One structure using multiple material samples is a microfabricated arraycontaining “microhotplates”. The microhotplates act as miniature heatingplates for supporting and selectively heating material samples placedthereon. U.S. Pat. No. 5,356,756 to Cavicchi et al and U.S. Pat. No.5,345,213 to Semancik et al. as well the article entitled “KineticallyControlled Chemical Sensing Using Micromachined Structures,” by Semancikand Cavicchi, (Accounts of Chemical Research, Vol. 31, No. 5, 1998), allillustrate the microhotplate concept and are incorporated herein byreference. Although arrays containing microhotplates are known, theyhave been used primarily to create varied processing conditions forpreparing materials. A need still exists for an array-based sensorsystem that can actually characterize material properties.

It is therefore an object of the invention to provide a materialscharacterization system that can measure properties of many materialsamples quickly, and in some embodiments simultaneously.

It is also an object of the invention to construct a materialscharacterization system having a modular structure that can be connectedto a flexible electronic platform to allow many different materialproperties to be measured with minimal modification of the apparatus.

SUMMARY OF THE INVENTION

This invention provides an apparatus (or system) and method for testingmaterials in an array format using sensors that contact the materialsbeing tested. Accordingly, the present invention is directed to anelectronically-driven sensor array system for rapid characterization ofmultiple materials. A plurality of sensors are disposed on a substrateto form a sensor array. Properties that can be measured include thermal,electrical and mechanical properties of samples. Regardless of theproperty being measured or the specific apparatus, the materialscharacterization system of the invention includes multiple sensorscarrying multiple samples, means for routing signals to and from thesensors, electronic test circuitry, and a computer or processor toreceive and interpret data from the sensors. In a preferred embodiment,a modular system is constructed including a single sensor array format,and signal routing equipment compatible with this format which can beused with multiple sensor types and multiple electronic test equipmenttypes, permitting maximum flexibility of the system while preserving thegeneral advantages of sensor array-based characterization.Alternatively, some or all of the different parts of the system may beintegrated together into a single physical component of the system.

The sensors can be operated in serial or parallel fashion. A wide rangeof electronically driven sensors may be employed, which those of skillin the art will appreciate provide the opportunity to design anapparatus or method for specific applications or property measurements.The environment in which the measurement is made by the sensor can becontrolled.

This invention allows for rapid screening of combinatorial libraries orlarge numbers of samples prepared by other means. This invention allowsfor property measurements that cannot be done optically. However,optical measurements may be made in conjunction with the sensor basedelectronic measurements of this invention. One potentially importantfeature is the speed of the property measurements made with thisinvention. Two independent reasons for this speed are that one canmeasure samples in parallel or with smaller sample sizes than withconventional measurement techniques. Moreover, automated samplehandling, array preparation and/or sensor operation allows for acompletely automated rapid property measurement system in accord withthis invention.

The materials characterization system of the present invention iscomputer controlled. The control program includes a series of programinstructions that implement and execute data gathering from the sensors,processing the data and making control decisions based on the data,supplying test equipment operational control instructions, performingsignal processing operations on signals (data) gathered from thesensors, and calculating an arithmetic value for selected materialproperties based on the gathered and processed data from the sensors.

Further preferred embodiments are defined by the dependent claims 2 to46.

Preferably, a microthin film membrane forming said sensors is a siliconnitride membrane, and said substrate supporting said silicon nitridemembranes in said sensor array is a silicon wafer.

Preferably, at least one sensor in said sensor array comprises: amicrothin film membrane supported by said substrate such that saidsensor array is an array of microthin film windows; a first wiredisposed on said microthin film membrane, said first wire acting as aheater and a first thermometer; and a second wire spaced apart from saidfirst wire and disposed on said substrate, said second wire acting as asecond thermometer.

Preferably, said microthin film membrane forming said sensors is asilicon nitride membrane, and said substrate supporting said siliconnitride membranes in said sensor array is a silicon wafer.

Preferably, said substrate is made of a polymer sheet, and said sensorarray includes a plurality of heater/thermometers disposed on saidpolymer sheet.

Preferably, said polymer sheet is a polyimide.

Preferably, said heater/thermometer is printed on said polymer sheet vialithography.

Preferably, said substrate is made of a poor thermal conducting materialthat is at least 100 microns thick, and wherein said sensor arrayincludes a plurality of heater/thermometers disposed on said material.

Preferably, said heater/thermometer is printed on a glass plate vialithography.

Preferably, said sensor array includes a plurality of thermometersdisposed on a top surface of said substrate, and said substrate includesa large area heater disposed on a bottom surface of said substrate.

Preferably, said substrate is made of a polymer sheet.

Preferably, said substrate is made from a material having poor thermalconductivity and is placed on a heater block, and wherein said sensorarray includes a plurality of temperature sensors disposed on thesubstrate such that a temperature difference between a first portion anda second portion of the substrate can be determined.

Preferably, said substrate is a glass plate.

Preferably, at least one sensor in said sensor array comprises: a samplesupport with a thermal measurement pattern disposed thereon; a gapbetween said sample support and said substrate for thermally isolatingsaid sample support from said substrate; and a plurality of bridgesconnecting said sample support to said substrate over said gap.

Preferably, said leads are deposited on said substrate, and wherein saidmaterial samples in said materials library are deposited on top of saidleads.

Preferably, said material samples in the materials library are depositedon said substrate, and said leads are deposited on top of said samples.

Preferably, a generating means comprises a magnet that generates amagnetic field over the entire sensor array.

Preferably, said generating means comprises a magnet array having aplurality of magnets arranged in the same format as said sensors in saidsensor array, wherein each magnet in said magnet array corresponds witha sensor in said sensor array to generate a magnetic field over thecorresponding sensor.

Preferably, said sensors in said sensor array further measuretemperature, and said apparatus further comprises a plurality oftemperature controlled elements to impose a temperature gradient acrossat least one sample in said sensor array.

Preferably, at least one sensor in said sensor array comprisesinterdigitated electrodes disposed on said substrate.

Preferably, at least one sensor in said sensor array comprises: amechanical resonator formed on said substrate; and a piezoelectricmaterial deposited on top of said sensor to form an acoustic wavesensing electrode.

Preferably, said acoustic wave sensing electrode is operable in at leastone of a surface acoustic wave resonance mode, a thickness shear mode,and a flexural plate wave resonance mode.

Preferably, said acoustic wave sensing electrode acts as both amechanical resonator and a materials characterization device.

Preferably, at least one sensor in said sensor array comprisesinterdigitated electrodes disposed on said substrate.

Preferably, at least one sensor in said sensor array comprises: amechanical resonator formed on said substrate; and a piezoelectricmaterial deposited on top of said sensor to form an acoustic wavesensing electrode.

Preferably, said acoustic wave sensing electrode is operable in at leastone of a surface acoustic wave resonance mode, a thickness shear mode,and a flexural plate wave resonance mode.

Preferably, said acoustic wave sensing electrode acts as both amechanical resonator and a materials characterization device.

Preferably, the cantilever sensor is attached to a piezoresistor suchthat a deflection amount of said cantilever sensor is detected by achange in a resistance value of the piezoresistor.

Preferably said sensors in said sensor array are arranged in a formatcompatible with combinatorial chemistry instrumentation.

Preferably, said sensor array is an 8×8 array with a 0.25 mm pitch.

Preferably, said sensor array is an 8×12 array with a 9 mm pitch.

Preferably, said sensor array is a 16×24 array.

Preferably, said sensors in said sensor array are disposed on saidsubstrate in a planar arrangement.

Preferably, said sensors in said sensor array are attached to saidsubstrate via a plurality of sensor plates disposed in an array formatand extending generally perpendicularly from said substrate.

Preferably, said plurality of sensors in said sensor array are arrangedin a geometric shape.

Preferably, said geometric shape is a closed shape having straightsides.

Preferably, said geometric shape is a closed shape having curved sides.

Preferably, said geometric shape is a closed shape having both straightand curved sides.

Preferably, said geometric shape is an open shape having straight sides.

Preferably, said geometric shape is an open shape having curved sides.

Preferably, said geometric shape is an open shape having both straightand curved sides.

Preferably, said sensor array contains at least 48 sensors.

Preferably, said sensor array contains at least 96 sensors.

Preferably, said sensor array contains at least 128 sensors.

Preferably, said sensor array contains between 5 and 400 sensors.

Preferably, said circuit board in said standardized interconnectiondevice and said sensor array are coupled together via a connector, saidconnector being one selected from the group consisting of conductingelastomeric connectors, conducting adhesives, cantilever probes, stickprobes, wafer-to-board bonding, solder bump bonding, wire bonding,spring loaded contacts, soldering, and direct pressure connectionbetween contact pads.

Preferably, said circuit board and said sensor array are coupled throughone selected from the group consisting conducting elastomericconnectors, conducting adhesives, cantilever probes, stick probes,wafer-to-board bonding, solder bump bonding, wire bonding, spring loadedcontacts, soldering, and direct pressure connection between contactpads.

Preferably, said link is a multi-wire cable.

Preferably, said link is a wireless connection.

Preferably, said interconnection device comprises a signal routing meansfor selectively coupling a sensor or a group of sensors in said sensorarray to said electronic platform such that said electronic platformsends signals to and receives signals from said sensor array via saidsignal routing means.

Preferably, said link is a multi-wire cable.

Preferably, said link is a wireless connection.

Preferably, said interconnection device comprises a signal routing meansfor selectively coupling a sensor or a group of sensors in said sensorarray to said electronic platform such that said electronic platformsends signals to and receives signals from said sensor array via saidsignal routing means.

Preferably, the computer is managed by software that controls datacollection, data viewing, and user interface.

Preferably, said signal routing means selects a group of two or moresensors at a time for simultaneous analysis, and the apparatus furthercomprises two or more electronic channels connecting each of said groupof sensors to said electronic test circuitry, the number of electronicchannels being equal to the number of sensors in said group by saidsignal routing means.

Preferably, said automated material dispensing device are arranged in aformat compatible with combinatorial chemistry instrumentation.

Preferably, said automated material deposition device employs a methodselected from the group consisting of sputtering, electron beamevaporation, thermal evaporation, laser ablation and chemical vapordeposition.

Regarding the method of the present invention, further preferredembodiments are defined in the dependent claims 48 to 69.

Preferably the depositing step includes placing at least one material oneach sensor by vapor deposition to create the samples.

Preferably, the vapor deposition method is a combinatorial vapordeposition method that deposits two or more materials in varyingproportions on different sensors in the sensor array.

Preferably, the depositing step further includes the step of heating thesamples on the sensor array after they are placed on the sensors byvapor deposition.

Preferably, the environment that is changed is at least one selectedfrom the group consisting of humidity, temperature, pressure,illumination, irradiation, magnetic field and atmospheric composition.

Preferably, the input signal transmitted in the transmitting step is acombination of a linear ramp signal and a modulated AC signalsuperimposed on the linear ramp signal, and wherein the monitoring stepmonitors a modulation amplitude in the output signal and an averagevalue of the output signal.

Preferably, at least one sensor in the sensor array has a heater portionand a thermometer portion, the combined linear ramp signal and modulatedAC signal is transmitted through the heater portion, a DC signal istransmitted through the thermometer portion, and wherein the modulationamplitude in the output signal corresponds with a heat capacity of thesample and the average value of the output signal corresponds with anaverage temperature of the sample.

Preferably, the transmitting step transmits a linear ramp signal and anAC sinusoidal signal, and wherein the monitoring step monitors an outputsignal.

Preferably, at least one sensor in the sensor array has a heater portionand a thermometer portion, the linear ramp signal is transmitted throughthe heater portion and the AC signal is transmitted through thethermometer portion.

Preferably, a first frequency component of the output signal correspondswith the average temperature of the sample and wherein a secondfrequency component of the output signal corresponds with the heatcapacity of the sample.

Preferably, the loss of mass in the sample is due to at least oneselected from the group consisting of decomposition, burning, andoutgassing of reaction products.

Preferably, the measuring step measures a difference between the sampleon the top surface of the substrate and a bottom surface of thesubstrate, wherein the temperature difference corresponds to the heatcapacity of the sample.

Preferably, the heating step comprises the step of increasing thetemperature applied to the bottom surface of the substrate at a measuredrate, and wherein the measuring step comprises the step of comparing therate at which the sample temperature increases and the measured rate atthe bottom surface of the substrate.

Preferably, the measuring step measures a difference between the firstportion of the substrate and a second portion of the substrate, whereinthe temperature difference corresponds to the heat capacity of thesample.

Preferably, the heating step comprises the step of increasing thetemperature applied to the first portion of the substrate at a measuredrate, and wherein the measuring step comprises the step of comparing therate at which the sample temperature increases and the measured rate atthe first portion of the substrate.

Preferably, the method further comprises the step of measuring atemperature of the sample.

Preferably, the temperature and the complex impedance of the sensor aremeasured simultaneously.

Preferably, at least one sensor in the sensor array is a mechanicalresonator, wherein the depositing step includes depositing a samplematerial on the mechanical resonator and wherein measuring step includesthe step of transmitting an input signal to said at least one sensor tooperate the sensor in a resonance mode, and wherein the monitoring stepincludes the step of measuring a resonator response.

Preferably, at least one sensor in the sensor array is a mechanicalresonator, wherein the depositing step includes depositing a samplematerial on the mechanical resonator, and wherein the measuring stepincludes the steps of: placing the sensor array in a magnetic field; and

generating a resonance signal in the mechanical resonator; measuring anamount of damping in the resonance signal, wherein the damping amountcorresponds with the sample material's response to the magnetic field.

Preferably, at least one sensor in the sensor array is a mechanicalactuator, wherein the depositing step includes depositing a samplematerial on the mechanical actuator and wherein the monitoring stepincludes the step of measuring an actuator response.

Preferably, at least one sensor in the sensor array is a mechanicalactuator, wherein the depositing step includes depositing a samplematerial on the mechanical actuator, and wherein the measuring stepincludes the steps of: placing the sensor array in a magnetic field;measuring an amount of displacement in the mechanical actuator, whereinthe displacement amount corresponds with the sample material's responseto the magnetic field.

Preferably, the measuring step includes the steps of: passing currentthrough at least one sample; and measuring a voltage across the sampleto obtain the resistance of the sample.

Preferably, the measuring step includes the steps of: placing the sensorarray in a magnetic field; passing current through at least one sample;and measuring one or more voltages across the sample to obtain either aHall resistance, a magnetoresistance of the sample or both.

Preferably, the measuring step includes the steps of: heating or coolingone portion of at least one sample; measuring a first temperature at thefirst portion of the sample and a second temperature at a second portionof the sample; and calculating a temperature difference between thefirst temperature and the second temperature, wherein the temperaturedifference corresponds with a thermal conductivity of the sample.

Preferably, the heating step includes placing a heater or cooler at oneportion of the sensor array such that the sensor array has a heated orcooled portion and a non-heated or non-cooled portion.

Preferably, the heating or cooling step includes placing a heater orcooler at each sensor such that each sensor has a heated or cooledportion and a non-heated or non-cooled portion.

Preferably, the method further comprises the step of placing the sensorarray in a vacuum.

Preferably, the method further comprises heating or cooling one portionof at least one sample;

determining a first temperature at the first portion of the sample and asecond temperature at a second portion of the sample; and measuring avoltage difference across the sample, wherein the voltage difference andthe temperature difference corresponds with a thermopower of the sample.

Preferably, at least one sensor in the sensor array is a Hall effectsensor, and wherein the measuring step comprises the steps of: placingthe sensor array in a magnetic field;

measuring a response of at least one Hall effect sensor; and comparingthe response of said at least one Hall effect sensor containing a samplewith a reference Hall effect sensor that does not contain a sampledeposited thereon.

Preferably, at least one sensor in the sensor array is a cantileversensor, and wherein the measuring step comprises the steps of: placingthe sensor array in a magnetic field; and measuring an electrical signalcorresponding to said at least one cantilever sensor, wherein theelectrical signal corresponds to a deflection amount of the cantileversensor and the magnetic property of the sample material disposed on thecantilever sensor.

Preferably, the transmitted signal comprises a step or pulse and themeasurement step comprises monitoring the temperature change of thesample in response to the stepper pulse, and determining a thermal timeconstant.

Preferably, a single wire acts as both the thermometer and heater.

Preferably, the transmitting step transmits a linear ramp signal and anAC sinusoidal signal, and wherein the monitoring step monitors an outputsignal.

Preferably, a first frequency component of the output signal correspondswith the average temperature of the sample and wherein a secondfrequency component of the output signal corresponds with the heatcapacity of the sample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1E are diagrams illustrating the overall system of thepresent invention;

FIGS. 2A through 2D are diagrams illustrating examples of sensor arrayand contact configurations in the present invention;

FIGS. 3A and 3B are examples of a printed circuit board in theinvention;

FIG. 4 is one embodiment of a sensor array/circuit board assembly in theinvention;

FIG. 5 is a representative diagram of a matrix switch in the invention;

FIGS. 6A and 6B are representative diagrams illustrating twocontemplated sensor addressing schemes in the invention;

FIG. 7 illustrates one alternative contact structure for the sensorarray;

FIG. 8 illustrates another embodiment of the invention;

FIGS. 9A through 9C are examples of a sensor structure for thermalanalysis in the present invention;

FIG. 10 illustrates an alternative thermal analysis sensor substratestructure;

FIGS. 11A through 11F are sample traces of thermal analysis scansconducted according to the present invention;

FIGS. 12A through 12I illustrate one system for conducting thermalanalysis according to the present invention;

FIGS. 13A through 13G illustrate another system for conducting thermalanalysis according to the present invention;

FIG. 14 illustrates a thermal decomposition measurement according to theinvention;

FIGS. 15A and 15B illustrate dynamic thermal analysis conductedaccording to the present invention;

FIGS. 16A through 16E illustrate dielectric spectroscopy conductedaccording to the present invention;

FIGS. 17A and 17B show an example of a mechanical resonator structurethat can be used in the invention;

FIGS. 18A through 18C illustrate electrical transport characterizationconducted according to the present invention;

FIGS. 19A through 19C illustrate thermoelectric propertycharacterization conducted according to the present invention;

FIGS. 20A and 20B illustrate thermal conductivity characterizationconducted according to the present invention; and

FIGS. 21A and 21B illustrate magnetic property characterizationconducted according to the present invention.

FIG. 22 illustrates a thermopower property characterization conductedaccording to the present invention.

FIG. 23 illustrates the electrical circuitry used in the thermopowercharacterization example of FIG. 22.

FIGS. 24A-C graphically represent the data points generated or measuredduring the thermopower property characterization of FIG. 22.

FIG. 25 graphically illustrates an atomic composition versus thermopowercurve showing a comparison of the results of the present invention withresults from the Neisecke & Schneider study, 1971.

FIG. 26 illustrates a thermal conductivity property characterizationconducted according to the present invention.

FIGS. 27A-D represent the electrical circuitry and a plot of the datapoints for the thermal conductivity example illustrated in FIG. 26.

FIG. 28 illustrates a graphical representation of aluminum (“Al”) filmthickness versus thermal conductance for the example illustrated in FIG.26.

The abbreviation “abb.” as used in the drawings means arbitrary. Anarbitrary scale is most typically used in identifying prominent featuresin the heat capacity curve that are associated with phase transitions orother significant thermal events, and not the precise absolute value ofthe heat capacity.

DETAILED DESCRIPTION

Description of Apparatus

FIG. 1A illustrates the generic apparatus or system concept of thematerials characterization system of the present invention, and FIGS. 1Bthrough 1E illustrates possible variations of the system. Regardless ofthe property being measured or the specific hardware in the apparatus,the materials characterization system of the invention includes multiplesensors in contact with multiple samples, means for routing signals toand from the sensors, electronic test circuitry, and a computer orprocessor to receive and interpret data from the sensors or theelectronic test circuitry. FIG. 1B is a representative diagram of anapparatus where each component is separate and interchangeable, allowingmaximum flexibility and interchangeability of parts. FIGS. 1C through 1Eillustrate variations where portions of the apparatus, such as thesensor array and electronic test circuitry, are integrated into onepart, allowing for a more compact design, but with a greater degree ofcustomization of the apparatus for a particular application or propertymeasurement. Regardless of the degree to which components in theapparatus are integrated into one unit, the overall operation of thesensor-array based apparatus remains the same, as will be explained infurther detail below.

In one embodiment that those of skill in the art will appreciateprovides a great deal of flexibility, each sensor has adjacent to it aplurality of associated sensor contact pads. Alternatively, the contactpads can be arranged near the edges of the sensor array, with leads onthe substrate connecting the sensors to the contact pads, to prevent thecontact pads from being contaminated with the materials being tested.The system in this embodiment also includes a printed circuit boardhaving a plurality of board contact pads arranged in the sameconfiguration as the sensor contact pads in the sensor array.Connectors, such as conducting elastomers, stick probes, cantileverprobes, conducting adhesives, wafer-to-board bonding techniques, orother contact devices, couple the sensor array with the printed circuitboard by creating contacts between the sensor contact pads and the boardcontact pads, preferably the contacts are reversible and non-permanent.Thus, sensor arrays incorporating different sensor functionalities canbe created using the same array and contact pad format and contactedusing the same circuit board and connections.

The printed circuit board in the inventive system also includes tracesthat connect the individual contact pads to standard multi-pinconnectors placed near the edges of the board. This construction allowseasy connection between the printed circuit board assembly and the restof the system using standard multi-wire ribbon cable assembliescompatible with the chosen multi-pin connectors. In the system accordingto a preferred embodiment, the multiwire cables and connectors couplethe printed circuit board assembly to a multiplexer or other signalrouting means for selecting one or more sensors to be activated,depending on the specific software instructions to the signal routingmeans.

The multiplexer or signal routing means is, in turn, coupled to aflexible electronic platform, which can include electronic test andmeasurement circuitry, a computer, or both. The electronic platform canalso include a switch matrix, preferably under control of the computer,for connecting the multiplexer outputs to a variety of differentelectronics test instruments without manually reconnecting cables. Thus,when a sensor array incorporating a different sensor functionality isneeded, to test for a different material property, only minimalreconfiguration of the electronic platform is needed. In this manner,the same system can be used to test for a wide variety of materialproperties.

In other cases, it may be desirable to collect information from manysensors simultaneously, rather than in a rapid serial fashion. In thepreferred embodiment of the invention for such cases, the multi-wirecables and connectors themselves serve as the signal routing means andare directly attached to an electronics module having a multiplicity ofindependent electronics channels for driving and reading the sensors.The outputs of these independent channels are then collected by thecomputer.

The sensor array itself may contain different types of sensors designedto measure different material properties in the different operationmodes as well. Further, standardizing the sensor array configuration,the contact format, and the connections from the board to themultiplexer and/or the electronic platform allows easy “plug-and-play”interconnection as well as simplification of the sensor structuresthemselves. In one embodiment of the invention, no active circuitry isincluded in the sensor array, reducing the manufacturing cost of thesensor array enough to make the sensor array disposable, if desired.

The sensor array generally includes a plurality of sensors for measuringpreselected material properties or other properties that may be used incalculating an arithmetic value corresponding to a material property.The sensors are supported by a support member such as a metal or plasticsubstrate. In one embodiment, a contact pad is positioned adjacent thesubstrate. Alternatively, as discussed above, the contact pad may bepositioned at or near the edges of the substrate.

In a preferred embodiment, the sensor array has the same format as astandardized format used in combinatorial chemistry applications (e.g.,an 8×12 grid with 9 mm spacing in between each sensor). By using astandardized format, substances to be tested by the sensors incombinatorial applications can be placed on multiple sensorssimultaneously rather than one sensor at a time, e.g., via simultaneoustransfer from a standard microtiter plate, further increasing testingand processing speed in the apparatus.

The sensors in a single array can be constructed so that they allmeasure the same material property, or alternatively a single array cancontain several different types of sensors that measure differentmaterial properties. The modular format of the sensor array, thestandardized interconnection means, and the flexible electronic platformallows a great deal of flexibility in determining what types of sensorsto include in the array since the same general electronic platform (e.g.electronic test circuitry and computer) and array format is used,regardless of the specific property being measured.

Alternatively, the sensors can be suspended at the end of an array ofrods or plates that hang vertically from a common supporting plate,preferably in a standard combinatorial chemistry format, to form a“dipstick” array structure. The sensors can then be dippedsimultaneously into wells containing solutions of materials to becharacterized, wherein the materials to be analyzed are mixed with asolvent. After removing the dipsticks from the solutions and allowingthe solvent to evaporate, the sensors remain coated with a film of thematerial to be characterized.

The material can then be tested in the same manner as the sensors in theflat sensor array. The materials or liquids can also be tested while inthe wells. Other embodiments of the invention include integrating theprinted circuit board with the signal routing parts and/or theelectronic test circuitry to construct a more customizedcharacterization device or placing all components and electroniccircuitry on the same substrate as the sensors.

FIGS. 2A, 2B and 2D illustrate one example of a sensor array and contactpad layout pattern using an 8×8 square array with a 0.25 inch pitch(spacing between the centers of adjacent sensors in the array). Thisparticular two-inch square sensor array is compatible with vapordeposition chamber equipment that is often used in combinatorialchemistry and combinatorial materials science applications.

Another widely used combinatorial configuration is an 8×12 rectangulararray with a 9 mm pitch, shown in FIG. 2C. The specific sensor arrayconfiguration is selected to be compatible with, for example, theautomated deposition equipment being used and/or the physicalconfiguration of the material libraries being tested. A standardizedsensor array configuration allows material deposition apparatus todeposit entire rows, columns or an entire library of samples on all ofthe sensors in the array simultaneously, which is generally moreefficient than depositing materials one sensor at a time. The specificmaterial deposition method used depends on the material properties beingmeasured and the physical characteristics of the material itself. Forexample, in some thermal analyses, it is desirable to dissolve thematerial to be characterized in a solvent, deposit solution onto thesensor, and let the solvent evaporate to leave a film of material on thesensor's surface.

In some embodiments, it is possible to modify silicon-nitride membraneusing a silanization process to improve confinement of the solution tothe well. Silanization involves applying a surface coating that willeither attract or repel the deposited solution. A typical material is aperchloro-silane compound that when applied to the surface of the sensorarray, bonds to the surface and modifies the surface's wettability.Application is made by immersing the sensor array into a solution of asolvent and the perchloro-silane compound. In the case of siliconnitride membranes on a silicon substrate, the higher affinity of thecompound to bond to the silicon than the nitride changes the wettabilityof the edge of the well. This has the effect of confining the droplet inthe well as it is repelled from the edges of the well. This can be usedto confine the liquid droplet inside a well and allow much largervolumes of liquid than the well can hold normally. This technique may bealso applied to other substrates such as metals, glasses or polymerssuch as Kapton®. By selectively treating the surface of a material suchas Kapton® and leaving untreated dots in the area of the sensor, liquidconfinement can be implemented without physical wells.

For other materials, it may be more appropriate to place material thatis in the form of a slurry or powder directly on the sensor. Samplethickness on the sensor may depend on the testing method, the sampleitself or the method of sample deposition. Throughout thisspecification, the terms “thin” and “thick” may be used when referringto films, however, those terms are not meant to be limiting.

Referring to FIGS. 2A and 2B, the sensor array 10 includes a pluralityof sensors 12 and a plurality of sensor contact pads 14 corresponding tothe sensors 12. The specific micro-structure of the sensor 12 depends onthe material property or properties that the sensor 12 is designed tomeasure. Sensors 12 that are designed to measure different propertieshave different micro-structures. More detailed descriptions of theactual sensor 12 structure are provided below in the ExperimentalExample sections with respect to sensors that measure specific materialproperties. To the naked eye, however, the sensors 12 may look likesmall pads or tiny wells, depending on the specific materialcharacterization application, that are arranged on a planar substrate16; the functional differences are within each individual sensor 12 atthe microscopic level. More importantly, different sensor arrays 10,incorporating different sensors 12, will share a common array 10 andcontact pad 14 format.

The electronic wiring and interconnection devices for sending sensordata to and from the sensor array 10 are arranged into a configurationthat is compatible with the sensor array 10 format. As a result,different sensor arrays 10 for use in the same materialscharacterization apparatus will have the same sensor locations and thesame overall wiring patterns for electrical connections; differentarrays 10 will look identical at a superficial level, even if theymeasure different properties. This sensor array 10 standardizationallows arrays 10 that measure completely different material propertiesto be electrically contacted using a single interconnection device,which is in turn attached to a flexible electronic platform.

As illustrated in FIG. 2B, the contact pads 14 are located immediatelyadjacent the sensors 12, and the sensors 12 and the contact pads 14 arearranged in electrical communication. The sensors 12 and sensor contactpads 14 are formed on the substrate 16 in any selected array format thatis desired. For example, they may be compatible with the materialdeposition machine being used. Any desired geometry can be achieved,such as lines, squares, rectangles, circles, triangles, spirals,abstract shapes, etc. Such geometric shapes can be considered to haveeither an open or closed shape with either straight or curved sides orboth. Any number of sensors 12 can be used, including 5 sensors, 48, 96or 128 sensors, and preferably from 5 to 400 sensors may be in one array10.

The material selected for the substrate 16 can vary depending on theapplication in which the sensor array 10 will be used, as will beexplained by examples below. Possible substrate materials include, butare not limited to, silicon, silicon nitride, glass, amorphous carbon,quartz, sapphire, silicon oxide or a polymer sheet. For example, thepolymer substrate may be a polyimide such as Kapton® from DuPont. Otherpolymer substrates may be used, including those selected from the groupconsisting of aramids (such as Kevlar®), polyester (such aspoly(ethyleneterephthalate), oriented films such as Mylar®, orpoly(ethylenenaphthalate)), epoxy resins, phenol-formaldehyde resins,polytetrafluoroethylene (such as Teflon®), polyacetal (such as Delrin®),polyamide (such as Nylon®), polycarbonates, polyolefins, polyurethanes,silicones, polysiloxanes and the like. Other materials can also be usedfor the substrate 16.

Substrates 16 used for thermal characterization and other testsrequiring thermal isolation of small amounts of sample material shouldhave the ability to be formed into a thin film or sheet that canwithstand the temperatures at which the materials will be tested. In athermal analysis application in which the sample material is a thinfilm, for example, the portion of the substrate 16 that supports thesample material is ideally between 0.1 and 25 micrometers thick or thesame order of magnitude as the thickness of a material sample, tominimize the effects of the heat capacity and thermal conductivity ofthe substrate 16 in the test results without making the substrate 16 toofragile to work with easily. In short, the optimum dimensions of thesubstrate 16 will depend on the characteristics of the specific materialchosen for the substrate 16 and the specific property or properties tobe characterized by the sensor array 10.

The sensors 12 and sensor contact pads 14 are preferably formed on thesubstrate 16 via lithography. The specific number and design of thelithographic layers will depend on the characteristics to be measuredand the particular sensor application. If possible, the number of layersis preferably as few as possible, for example less than four or fivelayers, to minimize the number of fabrication steps and reduce theoverall cost of the sensor array. The number of lithographic layers canbe kept to a minimum by creating sensors 12 that characterize only oneor two material properties and also by eliminating on-board controlcircuitry within the sensor 12 itself, if desired. More specific sensorstructures are explained in further detail below with respect to theexperimental examples.

Keeping the sensor array 10 manufacturing cost low makes disposabilityof the array 10 possible, if desired or necessary (e.g. after testinginorganic materials that may not be easily removed from the sensors).Further, if there is no on-board control circuitry that could be harmedunder extreme conditions on the sensor array 10, the sensor array 10 canbe cleaned after use by dipping the entire array structure into asolvent or acid or heating the sensor array 10 at a very hightemperature to remove sample material residue. The cleaned sensor array10 can then be reused. Of course, placing on-board electronics on thesensor array 10 or integrating the array with a circuit board havingelectronic components is also an option, if deemed appropriate for theapplication in which the array 10 will be used.

In one embodiment, eight sensor contact pads 14 are provided for eachsensor, as shown in FIGS. 2A, 2B and 2D. For identification purposes,the eight pads can be divided into four pairs labeled A through D, witheach pair having a H (high) contact pad and a L (low) contact pad asbest seen in FIG. 2D. Using this labeling scheme, each sensor contactpad in the sensor array can be identified by an array position, aletter, and a H or L designation (e.g., (1,1)AH). Of course, othersensor 12 and sensor contact pad 14 configurations are possible as wellas alternative sensor contact pad identification systems. Also, in thisexample, the sensor contact pads 14 are preferably spaced at a {fraction(1/16)} inch pitch with a 1 mm spacing in between adjacent columns ofpads 14. This physical arrangement is particularly suited for couplingthe sensor contact pads 14 to a printed circuit board 30 via elastomericconnectors, which will be explained in greater detail below. Othersensor contact pad 14 arrangements can also be used, depending on thespecific manner in which the sensor array 10 will be electricallycontacted and the specific application in which the sensor array 10 willbe used, without departing from the scope of the invention.

FIGS. 3A and 3B are top views of a specific embodiment of a printedcircuit board 30 to be coupled with the sensor array 10 shown in FIGS.2A and 2B, and FIG. 4 shows an exploded view of one portion of anapparatus that connects the sensor array to the circuit board 30 in theinventive materials characterization device.

The circuit board 30 used in the examples (except for the dielectricexample) measures 11 inches in diameter and includes 8 layers ofmetallization. Gold was used for the top layer of metallization toobtain good electrical contact with elastomeric connectors. All eightlayers are super-imposed in FIG. 3B. Of course, this specific design canbe modified by those of skill in the art without departing from theinvention.

Generally, the printed circuit board 30 preferably includes a pluralityof board contact pads 32 having an arrangement which is a mirror imageof the arrangement of the sensor array contact pads 14, such that whenthe sensor array 10 is connected to the printed circuit board 30, thereis a one-to-one correspondence between the board contact pads 32 and thesensor contact pads 14. Tolerances in the positioning of the pads andtrails of 0.001-inches can be easily attained with modern manufacturingtechniques, permitting precise matching of the sensor and board contactpad patterns. The sensor contact pads 14 and the board contact pads 32,via leads 33 and connectors 34 that are disposed on the board 30, arethe primary contact points through which the sensor array 10 connectswith a flexible electronic platform, such as a computer and/orelectronic test circuitry.

To connect the sensor array 10 to the printed circuit board contact pads32, a plurality of Z-axis connectors 40 can be used, as shown in FIG. 4.The Z-axis connectors 40 create the electrical connection between thesensor contact pads 14 and the board contact pads 32. In the embodimentshown in FIG. 4, the Z-axis connectors are formed from rubber or otherelastomeric strips containing conductive metal particles or wires forcarrying current. These elastomeric conductors are preferably designedto conduct electricity in only one direction to prevent cross-talkbetween closely spaced contacts. Other possible connectors that can beused to couple the sensor contact pads 14 with the board contact pads 32include cantilever or stick probes or other types of spring-loadedcontacts, conducting adhesives, glues or epoxies, wire bonding,soldering, or direct contact between the sensor array and board contactpads 14, 32. Regardless of the specific type of structure, the Z-axisconnectors 40 must create a reliable connection between the sensorcontact pads 14 and the board contact pads 32, even when very closelyspaced together, to ensure reliable coupling between the sensor arrayelectronic platform without cross-talk between adjacent contact pads.

The Z-axis connectors 20 can be placed in a frame or positioning fixture42 that may be attached to the circuit board 30, as shown in FIG. 4.This allows the sensor and board contact pads 14, 32 to be lined up witheach other precisely and coupled through the Z-axis connectors 40 in aone-to-one relationship. In an alternative embodiment, the positioningfixture 44 may be modified with one or more cavities for receiving afluid for either heating or cooling the entire array. For instance, acryogenic fluid may be circulated through or applied to the fixtureresulting in a cooling of the array to subzero temperatures.Alternatively, the fixture 42 can be heated by circulating a heatingfluid, such as a glycol, through the cavities or by applying a resistiveheating element to the fixture. In a preferred embodiment, temperaturesranging between −195° C. and 200° C. have been achieved. One of skill inthe art will appreciate that fluids and heating elements capable ofobtaining temperatures outside the stated range may be used withoutdeparting from the scope of the invention.

The positioning fixture used with elastomeric connectors in the exampleexperiments discussed below had a square cavity, 2.002-inch +/−0.001″tolerance, for precisely positioning of the sensor array 10, slots 41 tohold the connectors 40, and holes 43 for optical/atmospheric access. Theconnectors 40 in the example experiments discussed below wereelastomeric connectors, such as Fujipoly “Zebra Silver” connectors,having dimensions of 1 mm wide, 2″ long, and 5 mm high.

A compression plate 44 can be used to provide additional security in theconnection between the sensor and board contact pads 14,32, especiallyif the sensor array 10 and the printed circuit board 30 are not bondedtogether. The compression plate 44 is simply placed on top of the sensorarray 10, secured in place with screws or other fasteners 46 andtightened until the sensor array 10, the Z-axis connectors 40 and theprinted circuit board 30 are pressed firmly together. The compressionplate 44 may have a plurality of holes 48 having the same configurationas the sensors 12 in the sensor array 10 to allow optical testing of thesensor array 10, either alone or in conjunction with the electricalcharacterization according to the present invention, if desired, andpermit gas exchange or evacuation. Holes 49 may also be provided in theprinted circuit board 30 for the same purposes.

The printed circuit board 30 may provide the primary electronic linkbetween the sensors 12 and any peripheral devices used to control andmonitor the sensor array 10, such as the components in the flexibleelectronic platform. The printed circuit board 30 also can, in manycases, be considered part of the signal routing equipment (as opposed tobeing considered a part of the sensor array 10). In the embodiment shownin FIGS. 3A and 3B, as noted above, the printed circuit board 30 has aplurality of connectors 34 arranged around the board's 30 periphery,leaving enough space in the center area of the printed circuit board 30for positioning the sensor array 10. The connectors 34 on the printedcircuit board 30 are preferably standard multiple-pin connectors so thata commercially available ribbon cable wire assembly can route signals toand from the sensor array 10 or couple the printed circuit board 30 withperipheral devices, such as a multiplexer and flexible electronicplatform. The illustrated structure, which was used in the examplesdiscussed below, is a Robinson-Nugent P50E-100TG 100-pin connector thatis compatible with the inputs of the multiplexer, but any othermultiple-pin connector can be used without departing from the spirit andscope of the invention.

Each board contact pad 32 has an associated lead 33 that extends fromthe board contact pad 32 to a pin on the connector 34. It should benoted that the connection between the printed circuit board 30 and theelectronic platform need not be a physical connection, such as a ribboncable, but can also be any type of wireless connection as long assignals can be transmitted between the sensor array 10 and theelectronic platform.

A multiplexer as illustrated in FIGS. 12D and 15B may be included in theapparatus as signal routing equipment linking the sensor array 10 andthe electric platform or test equipment being used, which isschematically represented in FIG. 6A. The multiplexer used in theexperimental examples discussed below was an Ascor model 4005 VXImultiplexer module, containing four custom Ascor switch modules (model4517). Each switch module contains 64 2-wire relays, in eight groups ofeight relays per group, for a total of 128 input connections per module(512 connections total, corresponding to the number of contact pads onthe sensor array). This design was chosen because it was easy tointegrate with the embodiment having an 8×8 array with 8 contact padsper sensor. Thus, it will be apparent to one skilled in the art thatdifferent designs may be used without departing from the invention. Eachswitch module also has four output connections, which can be connectedto different input connections by closing selected relays under computercontrol. The signal routing equipment shown in FIG. 6A emphasizessimultaneous contact and connection of all of the sensors 12 tomultiplexer inputs, with sensor selection being conducted by closingselected switches in the multiplexer.

A preferred embodiment facilitates attachment of standard electronictest and measurement equipment to the outputs of the signal routingequipment. For the experimental examples discussed below, there wereeight terminals, one for each contact pad 14 on the sensor 12. Theoutputs were routed to a panel containing standard panel-mounted BNCcoaxial connectors. However, again this design can be modified by thoseof skill in the art without departing from the invention. Generally, agiven pair of signals (e.g. AH and AL) can either be connected to acenter conductor and shield a single BNC terminal, which is electricallyisolated from the mounting panel, or be connected to the centerconductors of two separate BNC terminals whose outer shields areconnected to the system ground. This permits either single-ended or truedifferential connections to the sensors, with the connection mode chosenmanually for each pair of leads (e.g. A, B, C, and D) by means of atoggle switch. Thus, when a single sensor 12 is selected, the eightcontact pads 14 of the selected sensor 12 can be easily accessed fromthe panel of BNC connectors, using virtually any desired piece ofelectronic test and measurement equipment. Other types of terminals canof course be used.

For the apparatus used in the examples, thirty-two analog backplaneconnections were provided between multiple 4517 switch modules in thecommon 4005 multiplexer module, permitting highly flexible configurationof the multiplexer. In addition to permitting selection of one sensor ata time, the backplane connections permit selection of one sensor fromeach row at a time, with the outputs being made available on one or more32-terminal output modules, which are also housed in the 4005multiplexer module and are connected to the analog backplane. Theflexible multiplexer design also permits the multiplexer to be used witharrays larger than 8×8 by permitting additional switch modules to beinserted into the housing and connected to the common backplane.

Again for the example experiments, the Ascor 4005 multiplexer module washoused in a Hewlett-Packard model HP E8400A 13-slot VXI mainframe.Communication with a computer was through a National InstrumentsGPIB-VXI/C interface module, which allows control of the VXI system viathe computer's GPIB interface. The multiplexer was controlled from thecomputer by sending appropriate commands to the GPIB-VXI/C interfacemodule. The software for controlling the multiplexer preferably permitsoperation in two different modes. In both cases, a graphicrepresentation of the sensor array 10 was shown on the computer screenin the form of an array of “buttons.” In manual operation mode, the userselects one or more sensors by clicking on the corresponding buttons andthen instructing the computer to close the appropriate switches. Alleight connections to the selected sensor or sensors 12 are then closed,while any previously closed connections on non-selected sensors 12 areopened.

In automatic or scan operation mode, using the control software the useragain selects a group of sensors by clicking on the correspondingbuttons. The computer then closes the switches to the first sensor,performs a measurement procedure, and opens the switches to the firstsensor. The procedure is repeated for all of the sensors selected by theuser, scanning across each row from left to right and moving from thetop row to the bottom. Relays are not closed and measurements are notperformed on unselected sensors. This software can be changed toaccommodate preferred modes of operation, including running in parallel.

Once a sensor 12 is routed to the multiplexer output, many differentcommercially available electronics components may be connected to thesensor array 10 to input and output signals to and from the sensor 12.For example, if the sensor array is designed to measure resistance, aresistance meter that has one input is connected to the multiplexeroutput and can measure the resistance of any of the sensors 12 that areconnected to the multiplexer inputs. The multiplexer allows a user toselect any one of the sensors 12 on the array 10 and output data relatedto the resistance properties of the sample material containing theselected sensor 12.

Alternative signal routing equipment is illustrated in FIG. 6B. A probeassembly 61 having probes 63 disposed thereon in an arrangement thatmatches the sensor contact pad arrangement 14 on one or more sensors 12is position over a selected sensor 12 via a three-axis translationstage. The three axis translation stage is preferably controlled bymotors under computer control. The probe assembly 61 itself may bemoved, or the substrate 16 may be moved to position the assembly 61 andthe substrate 16 relative to each other. To select a sensor 12, theprobe assembly 61 is positioned over the selected sensor 12 and movedtoward the substrate 16 to make electrical contact with the selectedsensor's 12 contact pads. Wiring from the probe assembly connects theselected sensor or sensors to the electronic platform. The specifictechnology used for positioning the probe assembly 61 can be anypositioning mechanism known in the art. The advantage of the sensorselection and signal routing system shown in FIG. 6B is that it largelyreduces or eliminates the need for a circuit board, multiwire cables,and multiplexer.

FIG. 5 illustrates one possible configuration for a generic flexibleelectronic platform that can be used in conjunction with the sensorarray 10 of the present invention. In this example, the outputs from thesignal routing means 129, such as the multiplexer 126, are connected toa matrix switch 50 that is controlled by a computer 52. Thus, it will beappreciated that the computer 52 controls both The matrix switch 50 hasa plurality of electronic test measurement instruments 54 that can becoupled to any or all of the multiplexer outputs. A user can selectwhich instruments to connect to particular sensors 12 in the sensorarray 10 by either inputting instructions into the computer 52 to openand/or close the matrix switch 50 connections by opening and closing theconnections manually, including manually rerouting cables that attachoutputs to electronic inputs. Thus, this particular type of flexibleelectronic platform can output and read many different signals requiredfor measuring many different material properties with different sensors,simply by changing the connections within the matrix switch 50.

Because the sensors 12 can be accessed using off-board circuitry, theinventive structure allows great flexibility in the manner in which thesensors 12 are addressed. If a multiplexer is not used to control sensor12 addressing, and if a separate electronics channel is provided foreach sensor 12 as the signal routing means 129, then all of the sensors12 in the array 10 can be monitored simultaneously, allowing rapidparallel characterization of entire material libraries. If a multiplexeris used, any channel from any sensor 12 can be made available for inputor output via its corresponding multiplexer terminal, and simultaneousbut separate of addressing individual sensors in different rows in thearray 10 is also possible. Alternatively, the computer 52 can also beprogrammed to conduct rapid serial measurement (addressing one sensor 12at a time), addressing all sensors 12 in a selected group simultaneously(such as heating each row to a different temperature to study thermalprocessing conditions), and simultaneously addressing one sensor 12 fromeach row (combined serial/parallel sensor measurement) as shown by thestructure illustrated in FIG. 6A. All of these sensor accessing schemescan be implemented electronically, through software instructions to themultiplexer, without physically reconfiguring or rewiring any part ofthe apparatus because of the apparatus' modular construction, theinterconnection structure, and the flexible electronic platform. Ofcourse, if desired, any or all of the components (e.g., the multiplexer,the printed circuit board 30, the sensor array 10, and the electronictest circuitry from the electronic platform) can also be integrated invarious ways to construct a more customized materials characterizationunit.

An alternative structure for the sensor array 10 is shown in FIGS. 2Cand 7. In certain applications, such as characterization of liquidmaterials, it is not desirable to have the contacts between the sensorarray 10 and the printed circuit board 30 located in the same vicinityas the sensors 12 themselves. The liquid materials would tend tocontaminate the contact pads 14, 32, reducing the integrity of theinterconnection between the sensor array 10 and the printed circuitboard 30 and preventing reuse of the interconnection hardware, such asthe Z-axis connectors 40. To overcome this problem, the sensor array 10shown in FIGS. 2C and 7 directs the leads from all of the sensors 12 tothe edge of the substrate 16, away from the actual sensor sites. Contactbetween the sensor array 10 and the printed circuit board 30 is made atthe edge of the substrate 16, either with Z-axis connectors 40 as in thesensor array described above or with probe cards or probe arrays 70(traces and connectors not shown), as shown in FIG. 7. Cantilever probes72 on the probe array 70 provide the electrical link between the sensorarray 10 and, for example, the multiplexer 126, the flexible electronicplatform, or some other peripheral device.

Because the sensors 12 in the sensor arrays 10 shown in FIGS. 2C and 7are relatively flat and have their top surfaces physically exposed, arubber gasket (not shown) containing holes in the same locations as thesensors can be placed on top of the sensor array 10 to hold liquids inplace over the sensors 10. The gasket can be pressed or bonded to theplate while the traces connecting the sensor array 10 to the printedcircuit board 30 can still be run along the substrate 16 to its edge.Further, because there is a clear optical path to the sensors 12 from anoverhead vantage point, the sensor array 10 can be used in conjunctionwith a camera or other optical sensing device, allowing even morematerial properties to be measured simultaneously. For example, if thesensors 12 in the array 10 are designed to measure the progress of acuring process via measurement of material dielectric constants, using acamera in conjunction with the materials characterization device of thisinvention allows detection and measurement of exothermic propertiesand/or temperature changes at the same time as measurement of thedielectric constant, further increasing the number of characteristicsthat can be measured at one time. See WO 98/15805, incorporated hereinby reference, for a discussion of optical screening techniques.

An alternative structure for the present invention is shown in FIG. 8.In this embodiment, substrate 16 is coupled to a mounting plate 17,which incorporates wiring for communication and multiplexing. Theindividual sensors 12 are cut apart and mounted onto individual sensorplates 80 to form “dipsticks” 82 that preferably extend vertically fromthe substrate 16. The spacing and format of the dipsticks 82 may followa conventional combinatorial chemistry format, such as an 8×12 arraywith 9 mm spacing, so that all of the dipsticks 82 in the array 10 canbe dipped into standard combinatorial chemistry wells 84 simultaneously,as shown in FIG. 8.

In a preferred embodiment, the wells 84 contain solutions comprising thematerials to be characterized dissolved in a solvent. It will beappreciated that each vessel 84 may contain the same or differentsolutions for testing. Once the dipsticks 82 are dipped into the wells84 and removed, the solvent is allowed to evaporate and the sensors 12are left coated with the sample material. Input and output signals arethen sent to and from the sensors 12 in the same way as described aboveto characterize the material properties. The liquids in the wells 84 canalso be directly characterized as the while the sensors are immersed inthe wells 84.

Because the materials characterization system of the present inventionhas a modular, flexible structure, many different material propertiescan be monitored simply by changing the sensor structures in the sensorarray 10 and attaching different electronic components to the arrayoutputs or signal router outputs as needed, depending on the specificmaterial property to be measured. Thus, the same interconnection methodand signal routing equipment may be used for all types of measurements,where the only components that need to be changed are the sensor array10 itself (“plug-and-play” operation) and possibly some specificelectronic test circuitry in the electronic platform. This is much lessexpensive than purchasing a separate machine for measuring eachproperty. Also, as can be seen below, the sensor arrays 10 themselvesmay be reusable in certain applications, reducing expenditures fortesting even further. The measurements obtained from the sensors 12 inthe sensor array 10 of the present invention can be directly correlatedto known testing results. In other words, the results obtained from thesensor arrays 10 correlate with results obtained from conventionalmaterials characterization methods. This advantage of the presentinvention will be highlighted in greater detail with respect to theexperimental examples described below.

Thermal Analysis Background

Thermal analysis is one of the most generally useful techniques ofmaterials analysis, particularly measurements of heat capacity. In manycases for thermal analysis, it is important that the sample beinganalyzed is thermally isolated from its environment to a large degree.Thermal isolation insures that heat flows into and out of the sample andthe associated changes in the sample temperature may be accuratelydetermined and are not masked by much larger heat flows associated withother objects, such as the sample holder or substrate, heater andthermometer, etc. Samples produced in combinatorial materials synthesismay consist of films, created by physical vapor deposition techniques(evaporation, sputtering, etc.) or by deposition of a liquid solution orsuspension and subsequent evaporation of the solvent. The samplespreferably have small lateral dimensions (e.g. 1 mm or less), to allowmore samples to be deposited on a given area. A sensor designed forthermal analysis of combinatorial libraries must therefore allowaccurate measurements to be made on very small samples that are packedclosely together on a substrate. Although thermal isolation of minutesamples initially poses a challenge, it also offers an advantage in thatthe thermal time constants for internal equilibration of the sample,heater, and thermometer are greatly reduced, permitting more rapidmeasurements to be made.

Thermal isolation of small-area thin film samples may be most easilyachieved by using a thin film of low thermal conductivity material tosupport the sample, where the support's thickness is comparable to orless than that of the sample. The heat capacity and thermal conductanceof the support are thus comparable to that of the sample film, can beindependently measured, and can be subtracted from measurements madewith a sample present. Further isolation during the measurement can beachieved by use of various modulated or pulsed heat capacity measurementmethods, which will be discussed below.

Issues affecting the design of a thin film calorimeter are the materialsused for fabricating the substrate and thin support membrane, thematerials used for fabricating the heater and thermometer, the geometryof the heater and thermometer, membrane, sample, and substrate as theyaffect the temperature profile and transport of heat, and the way inwhich the sensors can be connected to an interface so that usefulinformation can be obtained from the sensors. FIGS. 9A through 9Cillustrate preferred sensor structures for use in thermal analysisapplications with thin film samples. Although the figures illustrate thestructure of one individual sensor, it is understood that all or part ofthe sensors in the sensor array can be manufactured on the substrate 16simultaneously.

FIG. 9A is a preferred thin-film structure for conducting thermalanalysis of a thin-film sample 90. A micro-thin membrane 94, whichsupports the sample material 90, is preferably made of silicon nitride(Si₃N₄) on a silicon wafer substrate 92. The substrate 92 preferably hasa plurality of membranes 94 that are formed thereon in the desiredsensor array arrangement. To form the membranes 94, a thin film ofsilicon nitride 95 is deposited on the top and the bottom surfaces ofthe silicon wafer 92. The thickness of the silicon nitride film 95 ispreferably between 500 angstroms and 2 microns, as this thickness can beeasily produced by chemical vapor deposition and other techniques; italso corresponds to the typical thickness of the thin film samples 90 tobe studied. Nitride membranes having a thickness of 2 microns aregenerally preferred. Nitride membranes having a thickness of this amounttend to have improved durability with a tradeoff as to sensitivity. Anadditional benefit is improved consistency of temperature measurementacross the sensor array 10.

The desired membrane pattern is then created on the bottom surface ofthe silicon wafer 92 to open up “windows” 96 in the silicon nitride film95, exposing the silicon 92 at selected locations. The entire waferstructure is dipped into an etching solution, such as potassiumhydroxide, to erode or etch away the silicon 92 exposed through thewindows and form the structure shown in FIG. 9A. Regardless of thespecific etchant used, it should etch silicon but not etch siliconnitride. Because of silicon's crystal structure, the etching processforms a well 97 with sloping walls through the silicon layer 92 andwhich stops at the top silicon nitride layer 95. The resulting structureis a suspended, micro-thin silicon nitride membrane 94 supported bysilicon 92. The well 97 makes the sensor array structure particularlysuited for depositing films from solids dissolved in a solvent, as adrop of the solvent can be held in the well 97 during drying. The well97 can also contain liquids that are being tested.

FIGS. 9B and 9C illustrate one possible heater/thermometer pattern 100that can be printed on the membrane 94 to form a complete thermalanalysis sensor. As can be seen in the figure, the preferredheater/thermometer pattern 100 is designed so that the thermometerportion 102 is much smaller than the heater portion 104 and so that thethermometer 102 is located in the center of and surrounded by the heater104. The heater 104 is still sufficiently small so that the edges of theheater/thermometer pattern 100 are isolated from the edges of themembrane 94. These design features give the sensor 12 several desirableproperties that make it useful for conducting rapid heat capacitymeasurements on thin film samples. The time constant for equilibrationof the heater 104 with the thick part of the substrate 92 (beyond theedge of the “window”) is much longer (slower) than the time constant forinternal equilibration of the portion of sample 90 adjacent to theheater 104 and thermometer 102, since the time constant is proportionalto the square of the distance over which the heat must diffuse. Thetemperature profile across the heater 104 may to some extent have anon-uniform dome-shaped profile due to heat flow from the center of theheater 104 outwards; placing a small thermometer 102 in the center ofthe heater 104 allows measurement of the temperature in a region whosetemperature is much more uniform than the temperature of the entireheater 104.

The heater/thermometer 100 is preferably printed on the flat side of themembrane 94 via lithography so that the sample 90 can be deposited onthe membrane 94 within the “well” portion 97 and be characterizedwithout actually touching the heater/thermometer pattern 100. Themembrane 94 prevents direct physical contact between theheater/thermometer 100 and the sample, yet is still thin enough tocreate intimate thermal contact between the heater/thermometer 100 andthe sample 90 and allow heat to conduct through the membrane 95 to warmthe sample 90 and measure its thermal characteristics. This feature isparticularly useful when characterizing metals, where direct physicalcontact between the heater/thermometer 100 and the sample 90 wouldcreate a short circuit in the heater 104. Heater/thermometer leads 106are connected to the sensor contact pads 14 or are otherwise configuredfor coupling with the flexible electrical platform so that the powerinput and the sample's temperature can be monitored and controlledelectrically. Thus, it can be seen that in some embodiments, coatingsmay be used on the sensors to protect the sensors from the samples orvice versa.

The specific configuration for the micro-calorimeter array and thesystem architecture for coupling the sensors 12 in the array 10 to theelectrical platform can be any structure desired by the user as long aselectrical signals can be sent to and read from each individual sensor12 in the array 10. The micro-calorimeter used in the exampleexperiments was custom manufactured so that the substrate 92 was a 0.5mm silicon wafer, with 0.5 μg of low-stress LPCVD silicon nitridedeposited on both sides. The silicon nitride membranes 94 were 2 mmsquares and prepared by known procedures. To produce the metallizationpatterns, a liftoff procedure was used. Photoresist is spun on to thefront side of the wafer, and is patterned by photolithography using astepper. 50 Å of Ti was then deposited on the photoresist and theexposed portions of the substrate, followed by 2000 Å of Pt. The Tilayer was added for adhesion purposes. The photoresist was thendissolved, leaving metal in the desired pattern on the substrate. In theembodiment of the heat capacity sensor used in the examples, the heater104 consists of a serpentine pattern, with 60 μm lines separated by 20μm spaces. The thermometer 102 is a smaller area serpentine pattern,with 20 μm lines and 20 μm spaces. Following liftoff, the wafer was cutinto the form of a square measuring 2.000″ +/−0.001″ precision, using adicing saw. Accurate dicing of the wafer is needed for accuratepositioning of the wafer relative to the circuit board, using thepositioning frame. A dimension of 2″ was chosen to allow the substratesto be inserted into combinatorial vapor deposition equipment.

An alternate material for the substrate 16 is a polymer sheet. Aparticularly suitable polymer is a material called Kapton®, which ismanufactured by DuPont. Kapton® is thermally stable and can withstandtemperatures up to 350-400 degrees C without deterioration. Kapton® isoften sold in sheets ranging from 6 microns thick to 100 microns thick,and the heater/thermometer design, such as that shown in FIGS. 9B and9C, can be printed directly onto the film via lithography or othertechniques. To suspend the Kapton® sheet when conducting thermalanalysis, the contacts can be printed such that they are all at theedges of the sheet, as shown in FIGS. 2C and 7, and the sheet can bestretched and clamped at the edges to connect the contacts on the sheetwith corresponding contacts associated with the flexible electronicplatform.

Sensor arrays are fabricated on 12.5 and 25 micron Kapton® films usingstandard lithography techniques and metal films such as gold orplatinum. Arrays are bonded to a rigid metal substrate with circularholes to produce a format compatible with substrates such as silicon. Asubstrate of metal such as aluminum or copper is used. For bonding,adhesives such as epoxies chosen for thermal and chemical compatibilitywith the materials to be tested are used.

The substrate is fabricated with openings on the same spacing as theKapton® sensor array elements and bonded together. The resultingstructure of the substrate and Kapton® film form a well or cavity intowhich samples may be deposited. In the case of thermal sensors,electrical connections are located on the opposite side of the array andthus electrically isolated from the samples. The Kapton® film servesboth as the membrane for the sensor as well as electrical insulation ofthe traces from the substrate and sample while maintaining thermalcontact essential for the measurement. The openings in the substrate maybe fabricated as circular, square, rectangular or any convenient shape.Circular openings are optimal for liquid deposition due to the circularshape of liquid droplets.

If the samples are not electrically conducting, then the entire side ofthe sheet opposite the side containing the sensors can be covered with alayer of metal, which can be used as a blanket heater for heating all ofthe samples simultaneously, either via a DC signal or a modulatedsignal. As noted above, the inventive structure provides enoughflexibility so that selected samples can be heated individually,simultaneously, or in any grouped combination simply by changing theelectronic signals sent by the electronic platform.

In applications where larger amounts of material are available foranalysis, e.g. samples which may be 10's to 100's of micrometers thick,it may be possible to use thicker substrates. In these cases, thermalisolation can be improved by using substrates with low thermalconductivity, such as glass, or by micromachining a gap or “moat” 110around a sample support 112, which is spanned only by microbridges 114of material, as illustrated in FIG. 10. The heater/thermometer patternmay be printed on the sample support 112. The microbridges 114 hold thesample support 112 in place on the substrate while minimizing heatleakage, and also act as supports for wires which must pass into and outof the sensor for coupling with the electronic platform.

Experimental Example: Thermal Analysis of Polymers and Metal Alloys

The modular sensor array structure described above is particularlyuseful for rapidly measuring thermal properties of combinatoriallysynthesized libraries of polymers. The predominant use of heat capacitymeasurements with polymers is for the determination of the temperaturesat which phase transitions occur and the identification of the types ofphase transitions occurring (generally either glass transitions ormelting points). This information can then be used in two general ways.

In some specific cases, it is desirable to have a phase transition occurat a particular temperature, and the goal of combinatorial synthesismight in part be to tune the polymer's physical properties until thatvalue is achieved. For example, the glass transition temperature is animportant parameter for the polymer particles used in latex paints, asit strongly affects how the latex particles will coalesce and form afilm under given environmental conditions. A latex for a given coatingapplication may have to fulfill many other conditions as well, relatedto properties such as adhesion and weatherability.

It is a common practice to try to achieve several desirable propertiessimultaneously by making random copolymers, containing an essentiallyrandom sequence made from two or more different monomers. The types andnumbers of monomers used and their relative proportions can be varied inmany different combinations, to attempt creating a polymer thatsimultaneously fulfills all of the desired criteria. However, adding amonomer that improves adhesion may reduce the glass transition to anunacceptable value, for example. Thus, being able to rapidly measure theglass transition temperature (in addition to other properties) for manyhundreds of random copolymers allows the balancing of different physicalproperties to be done much more rapidly.

An example is shown in FIG. 11A, where the glass transitions have beendetermined for a series of styrene-co-butyl acrylate random copolymerswith different styrene contents, using the specific details discussedabove. The example shown in FIG. 11A illustrates temperature (T) vs.heat capacity signal (HCS) data for 100% styrene having an increasingbutyl acrelate content as shown by line 19. The random copolymers weresynthesized by Atom Transfer Radical Polymerization (ATRP) at 140 C for15 hours, using CuCl with two equivalence of4,4′-dinonyl-2,2′-bipyridine (dNbpy) as the control agent and(1-chloro)ethyl benzene (PhEtCl) as the initiator. The monomers styrene(S) and n-butyl acrylate (BA) were combined to make 11 solutions rangingfrom 100% S to 100% BA in steps of 10 volume %. A catalyst stocksolution was made in toluene by combining 1 part PhEtCl with 1 part CuCland 2 parts dNbpy. For each of the 11 monomer stock solutions were setup five polymerizations with varying ratios of monomer to initiator, byvarying the amount of catalyst stock solution added. This led to a 55element array of random co-polymerizations that varied in the x-axis bythe composition of monomers, and in the y-axis by the theoreticalmolecular weight (ranging from 10,000 to 50,000).

The samples in the example were chosen from the styrene-rich portion ofthe library, in order to produce Tg's above room temperature. Theexample of the inventive apparatus and method described here does notcontain a means for cooling samples below room temperature; however, asis obvious to anyone skilled in the art, this can be accomplished easilyin many different ways. The molecular weight of the polymers used wasapproximately 30,000 gm/mol. The polymers were dissolved in toluene atroom temperature to a concentration of approximately 2%. Small drops(approximately 5 μl) of the solutions were manually pipetted onto thesensors, and allowed to dry in air until a film was formed. The heatcapacity data shown in FIG. 11A were obtained using the inventiveapparatus and method, following the “3ω” measurement procedure, which isdiscussed below.

The glass transitions of the polymers can clearly be observed as a“step” in the heat capacity vs. temperature data. This is identical tothe type of behavior observed using traditional differential scanningcalorimetry to measure the heat capacity, and the data are of entirelycomparable quality with respect to the sharp definition of the featureassociated with the glass transition. The glass transition ofpolystyrene occurs near 100° C., in fair agreement with known results.It should be noted that these data were taken using an approximatecalibration for the temperature sensor; improved calibration procedureswill naturally yield more quantitatively precise values for Tg.

In addition, the glass transition temperature Tg can be seen to clearlydecrease to lower temperatures with increasing butyl acrylateincorporation. This is entirely in accord with the known behavior ofrandom copolymers, which typically show a glass transition temperatureat a value intermediate between that of the pure component polymers (a100% butyl acrylate polymer would have a glass transition temperature Tgof approximately −75° C.). However, the total time required to acquirethis data using the inventive method is less than 2 minutes. Similarmeasurements using a conventional differential scanning calorimeterwould take several hours or more.

Another example in which the precise value of a phase transitiontemperature is important is in the area of thermally responsivepolymers, including polymers with crystalline side chains, liquidcrystallinity, etc. Thermally responsive polymers are important to awide variety of applications. Thermal measurements on polymers are alsoimportant in determination of a polymer's performance under differentenvironments, including solvent, vapors, humidity, radiation, oxidationand the like. For example, the sample polymers may be tested afterexposure to a certain environment or may be tested while being exposedto the environment.

Even more generally, however, information about phase transitions cangive a great deal of insight into the chemical and physical structure ofthe polymer being studied, which in turn can be related either to thesuccess or failure of a particular synthetic strategy, or to thesuitability of the material for applications involving properties otherthan the melting or glass transition temperatures. Thus, thermalanalysis is extremely useful within a combinatorial polymer synthesisprogram, as it allows a scientist to rapidly assess variations inpolymer physical properties due to different catalysts, processconditions, etc, as well as to assess whether or not a polymer with adesired chemical composition or architecture has in fact beensynthesized. The following examples will illustrate these points.

Even in the case of polymers made from a single monomer (e.g. ethylene),the physical properties of the polymer will vary tremendously dependingon the architecture of the polymer, e.g. the molecular weight, and thedegree and type of branching. For example, high density polyethylene(HDPE) and paraffin (wax) are chemically similar, but differ in theirmolecular weights and the amount of bridging between crystallites. Thegreater number of chain ends in paraffin severely disrupts thecrystalline packing of the chains, in comparison to HDPE, leading tovastly inferior mechanical properties. The difference in physicalproperties is also directly manifested in a lower melting point forparaffin in comparison to HDPE.

Other factors which result in a reduced melting point are branching, andcomonomer incorporation. Branching not only reduces the value of themelting point, but also reduces the total degree of crystallinity.Crystalline polymers in fact consist of both crystalline domains, orcrystallites, and amorphous regions between the crystallites due tochain folding and chain ends. Generally, the greater degree ofbranching, the larger the amorphous fraction of the polymer. Theamorphous regions display a glass transition, and by measuring the heatcapacity signals associated with both the glass transition and themelting point, one can obtain information on the degree of crystallinityof the polymer, which in turn strongly affects the mechanical propertiesof the polymer. Similar considerations apply for polymers whichincorporate comonomers.

Thus, in evaluating combinatorial libraries of ethylene catalysts, arapid determination of the melting point and degree of crystallinity cangive a good qualitative picture of what type of polyethylene is beingproduced by the catalyst. This adds a great deal of information to lowerlevel screens such as the degree of catalyst activity and the polymermolecular weight, information which is more closely related to the enduses of the polymer produced by a given catalyst.

FIG. 11B shows heat capacity (HC) curves created with the apparatus ofthis invention for a series of ethylene-co-methyl acrylate randomcopolymers. The polyethylene-co-methyl acrylate copolymers used in theexperiment were purchased from Aldrich, and the Aldrich catalog numbers,the percentages of methyl acylate incorporation, and melting pointsaccording to the manufacturer were: #43076-5, 9% MA, MP=93° C.;#43264-4, 16% MA, MP=85° C.; and #43075-7, 29% MA, MP=48° C. Theethylene co-polymers were dissolved at a concentration of approximately5 wt % in trichlorobenzene, a high boiling point solvent, at 150 degreesC. Approximately 5 to 10 micro liters were dispensed onto each sensor 12and were kept in place by the naturally occurring wells beneath thesilicon nitride membranes 94. The solvent was allowed to air dry,leaving a polymer film 90 deposited on each membrane 94.

In the present example, the heat capacity data was obtained using the 2ωmethod, as described below. A broad peak in the heat capacity isobserved, marking the melting point. This peak is due to the latent heatassociated with melting of crystalline portions of the polymer and thedata are comparable to the results that may be obtained by traditionalDSC. The reduction of the value of the melting point and the degree ofcrystallinity with increasing methyl acrylate incorporation can beeasily seen in Figure 11B.

Heat capacity measurements can also be used to gain information on thearchitecture and microstructure of glassy (entirely non-crystalline)polymers. For example, a “random” copolymer of a given composition maybe either random or “blocky”, depending on whether or not the comonomersalternate in a random way or tend to occur in longer “runs” of a givenmonomer type. The degree of randomness or blockiness can affect the endproperties of the material. The degree of blockiness can be assessedthrough heat capacity measurements: a random copolymer tends to have asingle broad glass transition, at a temperature intermediate between theTg's of the constituent monomers. If the random copolymer is actuallyblocky, however, two distinct Tg's may be observed, corresponding todomains which form almost entirely from long runs of one or the othermonomer.

In a similar manner, heat capacity measurements can distinguish betweenimmiscible and miscible polymer blends or between phase-separated orphase-mixed block copolymers. Phase-mixed systems show a single Tg,while phase separated systems show two distinct Tg's. Even in the caseof a phase separated blend, small amounts of miscibility will occur,i.e., the two phases are not “pure”. This can also be assessed using Tgmeasurements, as the two Tg's will be somewhat shifted from the valuesfor the pure polymers.

The above examples illustrate the many ways in which thermal analysisdata can be used to gain important information on the structure andphysical properties of polymers. This information can be used toevaluate the success or failure of a particular synthetic route inmaking a polymer with a given chemical composition and physicalstructure/architecture; or to judge the suitability of a particularpolymer for a given application. Within the context of a combinatorialmaterials science approach to developing new polymer syntheticstrategies or new polymeric materials, in which many catalysts, processconditions, chain compositions and architectures, etc, will beattempted, it is highly desirable to be able to obtain thermal analysisinformation in a rapid fashion.

The sensor array method and apparatus of the present invention has asignificant advantage over other thermal analysis methods andapparatuses because it can characterize many different materialssimultaneously and quickly. Instead of obtaining only one heat capacityscan per unit time, the inventive method and structure can obtain tensor even hundreds of heat capacity plots in the same amount of time.Further, the sensor for this particular application obtains data thatcan be readily correlated with known data, e.g., from a conventionaldifferential scanning calorimeter (DSC), in that the heat capacity ofthe sample can be directly measured and plotted. Thus, the sensor outputneeds only minimal processing to generate data that can be easilyinterpreted.

DESCRIPTION OF THE METHOD FOR USING THE INVENTION

The method for utilizing the present invention is also simple, andfurther facilitates the rapid analysis of numerous samples. Once alibrary of, for example, 100 polymers is created via combinatorialmethods, each polymer may be deposited on the microcalorimeter sensorarray of the present invention to measure each polymer's thermalproperties. To form a sample 90, a small amount of solution containingthe polymer sample is placed on each sensor 12 and allowed to dry,leaving a film of the polymer behind. This can be done one sample at atime or multiple samples at a time manually or automatically, such as byusing a liquid dispensing robot with a single or multiple syringe tip.In a preferred embodiment, the sensor array 10 has a standardizedcombinatorial chemistry format so that the polymers may be depositedsimultaneously on multiple sensors 12 in the sensor array 10, usingknown combinatorial tools such as multiple syringe/multiple tippipettes, containing 4, 8, 12, or even 96 pipette tips possibly with thestandard 9 mm spacing.

Once the solvent has evaporated, leaving a polymer film sample 90 oneach sensor 12, the sensor array 10 is simply connected to theelectronic platform. This will be done, for example as shown in FIG. 4,by inserting the sensor array 10 in a positioning fixture 42 attached tothe printed circuit board 30 and applying pressure to the sensor arraysubstrate 16 by tightening screws 46 or other fasteners (such as clipsor clamps) on a compression fixture 44, insuring good contact betweenthe sensor array 10 and the printed circuit board 30. Preferably, theprinted circuit board 30 is housed in a chamber that can be evacuated.This eliminates heat losses to the atmosphere, and noise in thetemperature measurements due to convection. A heat capacity scan is thengenerated for each sensor 12 (typically in less than a minute),obtaining each material sample's crystallinity/amorphous properties,melting point, glass transition point, and other material characteristicinformation. The entire measurement procedure may be controlled andexecuted by a computer program in the electronic platform. Using thesoftware, the user initially specifies which samples in the array 10 areto be analyzed and provides other measurement information, such as thetemperature sweep rate and modulation frequency.

As a result, in this example, the heat capacity plots can be obtainedfor 100 samples in about 90 minutes or less, compared to around one ortwo samples in 90 minutes for known materials characterization devices,such as standard differential scanning calorimeters. By comparing andanalyzing the heat capacity plots of each material in the libraryquickly, a user can select which polymers in the library have the mostdesirable physical properties for a selected application or determinewhether or not a given synthetic strategy and set of startingingredients has in fact produced a polymer of a desired architecture andassociated physical properties.

Of course, thermal analysis is not limited to polymers. The same type ofanalysis can also be used to characterize inorganic solid statematerials, such as glasses, metal alloys, and compounds.

FIG. 11C shows an example using this invention of a glass transition(Tg) measurement in a thin film of low-Tg (400° C.) silica glassmanufactured by Ferro Corporation, type 7578 crystallizing solder glass.Such “solder glasses” are widely used as sealing or fusing materials ina variety of specialized electronics and other applications, and theability to rapidly measure Tg of different combinatorially synthesizedsilica glass formulations would be highly desirable in the developmentof new specialty glasses. The glass used in this example has a glasstransition temperature at approximately 395° C. according to themanufacturer. The glass is normally obtained in powder form, and thepowder was formed into a disk for this experiment by placing the powderin a mold and sintering at 450 degrees C for four hours. A 1 μm thickfilm was then deposited onto the sensor array using laser ablation. Themeasurements were made using the 3ω method, described below.

The present invention is also useful in the context of a search for newbulk amorphous metallic alloys, metals which do not have a regularcrystal structure, and which display a reversible glass transition muchin the same manner as silica glasses. Such materials are highlydesirable for their unique high strength and resiliency in comparison toconventional alloys. Amorphous alloys typically consist of three or moredifferent metal atoms, and achieving desirable physical properties suchas strong glass forming ability and a low Tg requires synthesizing manydifferent alloys with slight variations in composition. Thermal analysisis a widely used technique for analyzing the glass transition and otherphase transitions in candidate amorphous alloy materials. Thus, thecombination of combinatorial synthesis and rapid thermal analysis is apowerful technique which can be used in the search for new amorphousalloys.

FIGS. 11D and 11F show examples of the determination of melting pointsof several pure metals, and FIG. 11E shows a thermal analysis scan for acompound using the apparatus and method of this invention. The aluminumand lead films, each about 0.5 μm thick, shown in FIGS. 11D and 11F,respectively, were deposited on the sensors by RF sputtering, usingsingle element sputtering targets. The Al₃Mg₂ film was deposited as amultilayer film, using a combinatorial sputtering chamber. The film asdeposited contained alternating layers of 24 of AL and 26 of Mg. Thislayering was repeated 65 times, for a total film thickness of 3250. Thelayers mix to form the desired compound during the initial heatingstage, which is below the melting point. The results shown in FIGS. 11Dthrough 11F were obtained using the 3ω method, as described in thisapplication. Thus, the present invention, when combined withcombinatorial synthesis of thin solid films, can be used to map out theoutlines of entire binary, ternary, and higher order phase diagrams.This can be extremely useful in the search for new solid statecompounds, alloys, and other materials.

The method, which will be described in greater detail below, and theapparatus of the present invention, which has been described, can thusanalyze libraries of metal alloys, glasses, and other solid statecompounds and materials having varying compositions, to detect theoccurrence of important phase transitions. Again, because of the sensorarray 10 and library format used in the invention, a large number ofmaterials can be generated and screened in a short period of time. Inthe preferred method of deposition, the library of thin film materialsis directly produced on the sensor array substrate 16, usingcombinatorial masking and deposition techniques. See, e.g., WO 98/47613,incorporated herein by reference. Solid state films can also be producedfrom liquid precursors by sol-gel processes.

In short, material samples 90 are placed in intimate thermal contactwith the membrane 94 using vapor deposition techniques or by dissolvingthe sample in a solvent, depositing the solution on a sensor 12 andallowing the solvent to dry to form a thin sample material film on themembrane 94 of the sensor 12. The thinness of the membrane 94 and thesample 90 allows the sample 90 to be heated through very quickly, makingrapid scanning of the sample over a wide temperature range possiblewhile still obtaining clear thermal characteristic plots showing phasetransitions. This specific embodiment of the invention can scan overseveral hundred degrees and obtain heat capacity data for a given samplein 10 to 30 seconds, compared with 30 minutes to 2 hours forconventional calorimeters. This processing speed is further enhanced bythe invention's array format, allowing parallel or rapid serial scanningof multiple samples which are deposited on a single substrate, andincreasing the number of samples tested per unit time to as high as 64or more samples in 15 minutes.

Experimental Example: Thermal Analysis with Temperature Modulation

FIGS. 12A through 12H and FIGS. 13A through 13F illustrate thermalanalysis using temperature modulation. The preferred sensor structurefor conducting this type of analysis is the structure described aboveand shown in FIGS. 9A through 9C, but other thermal sensor structurescan be used without departing from the spirit of the invention. Thefollowing discussion of non-modulated calorimetry will provide anexplanation of the theory behind heat capacity measurements and willillustrate why temperature-modulated calorimetry is the preferred methodfor making heat capacity measurements with the sensors 12.

In an ideal or simplistic heat capacity measurement, all heat input intoa sample is retained by the sample, resulting in increases in thetemperature or change of the physical state of the sample. The heatcapacity can then be determined as the ratio between the rate of heatinput and the rate of temperature increase, C_(p)=ΔQ/ΔT. In reality,some of the heat input to the sample is continuously lost to theenvironment through conduction, convection, radiation, etc. In order forthe results of a heat capacity measurement to be meaningful, either someprocedure must be implemented to measure or account for the heat energylost to the environment, as is done in differential scanning calorimetryby means of an “empty cell” reference sample, or the rate at which heatis input to the sample must be much greater than the maximum rate atwhich heat is lost, so that losses may be neglected while maintaining agood approximation of the sample's heat capacity.

In the latter case, the entire measurement must be completed in a timeshorter than the thermal relaxation time t1 of the sample, where t1 isthe time that it takes for the sample to come to equilibrium at a newtemperature when the heat input level is changed to a new value. If theheat input is set to zero, t1 is the time constant for the sample toreturn to the temperature of the environment. The relaxation time isgiven by t1=C_(p)/k, where C_(p) is the heat capacity and k is thethermal loss constant to the environment. The reason for conducting arapid (less than t1) measurement is easy to understand: if the power issuddenly turned up to a certain level, the temperature will initiallyincrease rapidly and the losses to the environment will be negligible,since the sample is initially at nearly the same temperature as theenvironment. However, after a time of approximately a few times t1, thesample's temperature saturates or plateaus to a limiting value, as theheat input and losses to the environment become exactly equal. Thus,heat losses to the environment can be neglected only if the temperatureincrease is conducted over a time much shorter than t1.

For small, microthin samples, such as those tested in the invention, thetime constant t1 can be quite short, typically 0.1 seconds, due to thesample's very low heat capacity. The high temperature ramp rates whichmust be used with such samples in a “continuous sweep” calorimetryexperiment, e.g. 100's to 10,000's of degrees per second, make analysisof many phase transitions difficult or impossible, particularly in morecomplex materials. If a much slower ramp rate is used, then anequilibrium prevails between the heat input and the losses to theenvironment, and generally no information can be gained about the heatcapacity. Increasingly complex materials may take increasingly longtimes to complete structural rearrangements that occur at a phasetransition, which involve collective motions and rearrangements of manyatoms or molecules. Therefore, it is desirable to use a measurementmethod in which the heat capacity can be measured while the averagetemperature is varying at an arbitrary rate.

AC calorimetry, when combined with the sensor design of the invention,is a preferred way to obtain a rapid determination of heat capacityversus temperature with a minimum of off-line data analysis, but withoutrequiring prohibitively fast scanning of the average temperature.Although this discussion focuses on modulated calorimetry, othercalorimetric methods may be used in conjunction with the sensors orsystem of this invention, including methods based on measurements of thethermal relaxation time or methods in which the entire measurement isperformed in a time that is shorter than the thermal relaxation time,which are well known in the art.

The general concepts of AC calorimetry will now be explained inconjunction with FIGS. 12A and 12B, which are general to the concepts.In AC calorimetry, the power input to the sample consists of a slowlyvarying average value P(t), and a modulated part ΔP. The heater power(HP) modulation frequency 2ω (corresponding to modulation of the heatervoltage V_(H)(t) at a frequency ω, since P=V²/R) is chosen such that theperiod Δt=π/ω is much shorter than the time constant t1 forequilibration of the sample with the external environment, but muchlonger than the time constant t2 for internal equilibration between thesample, heater, and thermometer.

If the frequency ω is too low (ω<<π/t1), then the total power input isalways equal to the losses to the environment; in this case, thetemperature modulation is in phase with the power input modulation,contains information only about the thermal losses to the environment,and contains no information about the heat capacity. If the frequency ischosen so that ω>>/t1, however, the sample temperature modulation lagsbehind the power input modulation by a phase angle of 90°, because thereis insufficient time during a cycle for the sample to reach thetemperatures corresponding to the maximum and minimum power inputs. Thelarger the heat capacity of the sample, the more slowly it responds tothe power modulation, and the smaller the resulting temperaturemodulation will be. Under these conditions, the temperature modulationamplitude ΔT is given by ΔT=ΔP/2ωC_(p), where ΔP is the amplitude of thepower modulation and C_(p) is the heat capacity. Thus, the heat capacityis inversely proportional to the temperature modulation amplitude, for afixed ΔP. If the frequency is too high, however, i.e. ω>>π/t2, then theheater, thermometer, and sample are not in equilibrium with each other,and the thermometer thus does not give accurate information about theresponse of the sample temperature to the heater power input.

Thus, AC calorimetry generally involves measuring both the averagetemperature and the temperature modulation amplitude for a given sample,with an appropriately chosen frequency 2π/t1<<ω<<2π/t2, as the averagetemperature is varied. The heat capacity is given by Cp=ΔP/2ωΔT.

FIGS. 12C through 12H are explanatory diagrams of a particularembodiment of a heat capacity measurement system and measurement method,which uses the preferred sensor design discussed above and the ACcalorimetry technique. This particular embodiment is referred tothroughout this specification as the “2ω method”. FIGS. 12C and 12D arerepresentative diagrams explaining the 2ω method, while FIGS. 12Ethrough 12H show examples of input and output signals according to thismethod.

The voltage signal to the heater, V_(H)(t), is the sum of a slowlyvarying average value V_(H,0)(t) and a modulation v_(H)(t)=v_(H)e^(iωt)at frequency ω, i.e., V_(H)(t)=V_(H,0)(t)+v_(H)e^(ωt). The input poweris V_(H) ²(t)/R_(H)=[V_(H,0) ²(t)+2V_(H,0)(t)v_(H)e^(iωt)+v²_(H)e^(2iωt)]/R_(H), and contains modulations at frequencies of both ωand 2ω. The temperature of the sample is monitored by measuring theresistance of the thermometer 102, R_(TH)(t). In the 2ω method, this isdone by passing a small DC current I_(TH) through the thermometer 102and measuring the voltage V_(TH)(t). For many metals, the resistancevaries linearly with temperature, and can be parameterized by theformula R(T)=R(T=T₀)[1+α(T−T₀)], where α is a constant characteristic ofthe metal, and T₀ is an arbitrary reference temperature. Thus, thetemperature can be calculated directly from the thermometer voltage,using the formula T=T₀+[(V_(TH)/V_(TH)(T₀))−1]/α, if α, T₀ andV_(TH)(T₀) are known.

The average temperature and the temperature modulation at frequencies ωor 2ω can easily be determined over the course of an experiment by anumber of means. The average temperature is most easily obtained bypassing the thermometer voltage signal through a low pass filter 120with a suitable cutoff frequency, which removes the modulation,measuring the filtered thermometer voltage with an analog-to-digitalconverter, and calculating the temperature using the formula givenabove. The modulation is most easily and accurately measured using alockin amplifier 124, with the reference frequency set at ω or 2ωdepending on which frequency is being monitored. Other techniques canalso be used, such as an AC voltmeter with a narrow band pass filter onthe input, a spectrum analyzer, or direct recording of the waveform andsubsequent off-line analysis by fast Fourier transform.

It is preferred to monitor and analyze the signal at frequency 2ω. Theprincipal reason is that the power modulation ωP(2ω), given by v²_(H)/R_(H), varies relatively little during the experiment, varying onlydue to changes in the heater resistance R_(H) as the temperature isvaried. In contrast, the power modulation ΔP(ω)=2V_(H)(t)v_(H)/R_(H) iszero when the average heater voltage is zero, and varies over a muchwider range during the course of an experiment due to the lineardependence on V_(H)(t). This leads to vanishing sensitivity near thebase temperature, and a large variation in the signal-to-noise ratioover the course of an experiment.

The heat capacity is given by Cp=ΔP/2ωΔT, as described earlier. BecauseR_(H) increases with temperature, the input power modulation ΔP=v_(H)²/R_(H) decreases with increasing temperature. This leads to a decreasein the temperature modulation amplitude, independent of any changes inthe heat capacity. This must be accounted for in analyzing the data.Because ΔP is inversely proportional to R_(H), the heat capacity isproportional to 1/R_(H)ΔT, since v_(H) and ω are constant during a givenexperiment. Although R_(H) can in principle be precisely determined byan additional measurement, e.g., by monitoring the DC current drawn bythe heater in response to the DC voltage V_(H) and an absolute value ofCp determined, it is a reasonable approximation for many purposes toassume that the heater and thermometer are at the same temperature, andsubstitute R_(TH) (which is already being measured) for R_(H).

Thus, if one is only interested in identifying prominent features in theheat capacity curve that are associated with phase transitions or othersignificant thermal events, as is often the case, and is not interestedin the precise absolute value of the heat capacity, then the heatcapacity can be approximated (up to a multiplicative constant or scalingfactor) by 1/[<V_(TH)>ΔV_(TH)(2ω))], where the denominator is theproduct of the DC and modulated values of the thermometer voltage. Aplot of this quantity vs. the temperature (which is derived from V_(TH))captures all of the essential information in the heat capacity curve.More precise analysis methods may be used to obtain an absolute value ofthe heat capacity, without departing from the scope and spirit of theinvention.

It is now possible to explain more clearly why AC calorimetry, asembodied by the 2ω method, combined with the preferred sensor design,allows for such rapid measurements of heat capacity curves anddeterminations of phase transition points. A measurement of the heatcapacity at a given temperature requires measuring the modulationamplitude at that temperature. An accurate measurement of the modulationamplitude typically requires averaging or Fourier transforming over atleast several cycles. Five cycles, for example, is a reasonable minimumnumber. Thus, at a given temperature, an accurate determination of theheat capacity can be made in approximately 0.1 seconds for a typicaltemperature modulation frequency of 2ω=50 Hz. If it is desired to obtainone measurement per degree as the temperature is varied, for example,then the average temperature may be varied at a rate of approximately10° C. per second, or 600° C. per minute, compared to typical sweeprates of 10° C. per minute for conventional DSC instruments.

In practice, the temperature is not stabilized at a set of discretevalues while measurements are made at these values; rather, thetemperature increases continuously, and the modulation data can beconsidered a “running average” of the modulation amplitude over a finitetemperature range. This temperature range is typically several degrees,and is determined by the temperature sweep rate and the averaging timefor the modulation amplitude measurement.

Referring to FIG. 12C, using the 2ω method in the sensor array structureaccording to the present invention does not require any modification ofthe sensor structure itself because of the modular sensor arraystructure, standardized interconnection method, and flexible electronicplatform. As explained above, each sensor 12 in the sensor array 10 isconnected to a multiplexer 126 or other signal routing means 129, andboth the multiplexer 126 and the electronic test circuitry 127 fordriving the sensors 12 are controlled by a computer 52. The electronictest circuitry 127 and the computer 52 together can be considered aflexible electronic platform. To characterize materials on the sensors12 one at a time, the computer 52 controls the multiplexers 126 so thatit connects a given sensor 12 the electronic test circuitry 127. Theelectrical signals for a complete scan (as selected by the user) aresent to and read from the heater 104 and thermometer 102 on the selectedsensor 12, and then the multiplexer 126 switches the connection to linkthe electronics platform with the next sensor in the sequence. Thus, theinvention allows for ultimate flexibility in sensor array testing.

Sample results from a test conducted according to the 2ω method areshown in FIGS. 12E through 12H for illustrative purposes only. Morespecific details on the preferred manner in which the tests areconducted are as follows: The heater ramp voltage is obtained from anauxiliary analog output of an Stanford Research Systems SRS 830 lockinamplifier. This voltage is set via instructions to the lockin amplifierfrom the computer, transmitted over a GPIB interface. For the specificheater 104 design in the preferred sensor embodiment, a voltage rampfrom 0 to 1.5 volts is sufficient to raise the temperature of the sensorto approximately 150° C. (in vacuum). Higher maximum voltages result inhigher maximum temperatures. The ramp voltage is incremented by a smallamount (approximately ten times per second) and the size of theincrement can be specified by the user before beginning a scanningoperation. The size of the increment is typically in the range of fromabout 0.005 to 0.01 volts, so the total scan time is approximately 15 to30 seconds. When the maximum voltage is reached, the ramp voltage iseither ramped back down to zero at the same rate while taking data; orthe ramp voltage is set to zero and the scan is completed.

The heater modulation voltage is generated by the same lockinamplifier's sine wave oscillator output. Fundamental frequencies of10-40 Hz were generally used with the 2ω method, and a typicalmodulation amplitude is several tenths of a volt. The ramp andmodulation signals are added by a summing amplifier from OpAmp Labs,which also buffers the signals and supplies adequate current to drivethe heater, which has a 2-wire impedance of approximately 100Ω.

The DC current for the thermometer 102 was generated by connecting a 9Vbattery in series with a 10kΩ resistor and the thermometer 102,producing a current of approximately 1 mA. The use of a battery-poweredcurrent source insures that the thermometer 102 circuit is isolated fromground and from the circuitry connected to the heater 104. Thethermometer 102 resistance is measured in a 4-wire configuration, andthe 4-wire resistance at room temperature is typically 50 Ω. Thus, theinitial thermometer voltage is approximately 50 mV.

The thermometer voltage is then analyzed to extract the average value,which gives information on the temperature, and the modulationamplitude, which gives information on the temperature oscillationamplitude and the heat capacity. To measure the average thermometervoltage, the thermometer voltage is connected to the differential inputsof an SRS 560 low-noise voltage preamplifier with variable gain and aprogrammable filter. The preamplifier is typically used with a voltagegain of approximately 10, and a low pass filter set at 1-3 Hz to removethe modulation. The preamplifier output is connected to an auxiliaryanalog-to-digital converter input of the lockin amplifier, and thevoltage is read via instructions from the computer.

To measure the modulation voltage, the thermometer voltage is sent tothe differential inputs of the SRS 830 lockin amplifier, which is setfor signal detection at the second harmonic frequency of the sin wavebeing output from the oscillator. The second harmonic frequency is thustypically in the range 2f=20-80 Hz. The lockin input bandpass filter isset at 24 dB/octave, and a 0.3 second output time constant is typicallyused. Although phase-sensitive detection can easily be done, only thetotal magnitude of the modulation signal was recorded for simplicity.This is permissible if the frequency is properly chosen so thatt1>>π/ω>>t2, where t1 and t2 are the external and internal thermalrelaxation times discussed above.

The correct measuring frequency is chosen by measuring the modulationvoltage V_(th)(2ω) as a function of the drive frequency, and looking fora broad peak in a plot of ω*V_(th)(2ω) versus f=ω/2π, as is well knownto those skilled in the art of AC calorimetry. An example is shown inFIG. 12I, using the preferred sensors discussed above. At lowfrequencies ω<<π/t1, the temperature modulation amplitude ΔT andV_(th)(2ω) are independent of frequency, since a balance always prevailsbetween the modulated heat input and the losses to the environment. Inthis region, ω*V_(th)(2ω) increases linearly with Ω. In the optimalfrequency range for conducting calorimetry measurements, ΔT isproportional to 1/ω, as explained previously, so ω*V_(th)(2ω) isapproximately constant. At high frequencies ω>>π/t2, the thermometertemperature is out of equilibrium with the heater temperature, sincethere is insufficient time for heat to diffuse across the width of thethermometer during a single cycle. The temperature distribution over thethermometer takes the form of a damped travelling wave, with awavelength shorter than the size of the thermometer, and the averagetemperature and voltage modulation decrease as the frequency isincreased above π/t2. Thus a plot of ω*V_(th)(2ω) has the form of apeak, with the broad maximum indicating the optimum frequency range forperforming calorimetry measurements. Because of the breadth of the peakin this plot, it is not necessary to perform a frequency analysis foreach sample. Once it has been done for a given type of sample (e.g. aclass of materials with roughly similar film thickness and thermalconductivity), the same frequency can be used for all subsequentmeasurements on samples of that general type. In the example, 15 Hz ispreferred, but anywhere in the range of from about 5 to about 30 Hz maybe used.

Once the modulation frequency and amplitude have been set and all of thesignals are properly routed, numerous measurements can be rapidly madeusing a simple procedure. In the preferred embodiment of the procedure,a group of sensors is first specified for measurement via manual inputto the computer by the user. Once this has been done, the user instructsthe computer to begin an automated measuring procedure. All operationsdescribed below are performed automatically by the computer, followingparameters set by the user before the automated procedure is begun, suchas setting the ramp rate, etc.

The computer closes selected switches in the multiplexer so that thefirst sensor in the specified set is connected to the electronicsinstruments (current source, lockin, oscillator, etc.). It is desirableto wait several seconds for the electronics to settle after closing theconnections between a sensor and the electronic platform, to eliminatetransient responses.

The heater ramp voltage is initially zero. Before beginning to increasethe ramp voltage, the computer records the average thermometer voltage,which is defined as V(T₀). T₀ is the temperature of the sensor at thebeginning of the scan. This will be somewhat higher than roomtemperature due to the power dissipated in the heater by the modulationvoltage. In a preferred procedure, the modulation voltage is also set tozero before V(T₀) is recorded. It can then be assumed that T₀ is equalto the room temperature, provided that the heat dissipated in thethermometer 102 by the DC current causes only minimal self-heating.Various other procedures may be performed to determine more preciselythe sensor temperature at the beginning of the scan.

The modulation voltage is then turned on again, and the followingprocedure is iterated or looped approximately ten times per second: (1)measure the average thermometer voltage <V_(th)> and the modulationvoltage V_(th)(2ω); (2) calculate the temperature T using the formulaT=[<V_(th)>/V_(th)(T₀)−1]/α+T₀, where the coefficient α ischaracteristic of the metal which the thermometer is made out of and canbe determined separately by a variety of well known means. For Pt,typically α=0.0025−0.003; (3) calculate a quantity proportional to theheat capacity, referred to as the “heat capacity signal” C_(p), usingthe formula C_(p)=[<V_(th)>*V_(th)(2ω)]⁻¹, as discussed above; (4) storethe values of the time, the heater drive voltage V_(H), and the measuredand derived quantities <V_(th)>, V_(th)(2ω), T, and C_(p) in computermemory; (5) increment V_(H) to a new value; and (6) repeat steps (1)through (5). When the scan is finished, V_(H) is set to zero and thedata stored in memory are transferred to a file on a storage device. Thenext sensor is then selected by the computer and multiplexer, and theentire scan procedure is repeated.

An alternative AC calorimetry method that can be used in the inventionis the “3ω” method. For measurements concerning the thermal response ofpolymers, the 3ω method is preferred. FIGS. 13A and 13B arerepresentative diagrams explaining the preferred materialscharacterization apparatus configuration using the 3ω method, whileFIGS. 13C through 13F show examples of input and output signalsaccording to this method. In this method, the heater receives only aramped DC voltage V_(H,0)(t), instead of a ramped voltage with amodulated AC voltage superimposed thereon. Also in the “3ω” method, anAC current in the form of a pure sine wave at frequency co is sentthrough the thermometer instead of a DC current. The AC current throughthe thermometer preferably has a constant amplitude. Further, ratherthan measuring the 2ω modulation amplitude and the average value of thethermometer voltage to determine the sample material's heat capacity andtemperature, respectively, the 3ω method measures the third harmonic inthe thermometer voltage to determine the sample's heat capacity, asshown in FIG. 13E, and measures the first harmonic voltage to determinethe temperature, as shown in FIG. 13D and as explained below.

If the AC current amplitude is sufficiently small, or the sample's heatcapacity is sufficiently large, then the temperature of the sample doesnot vary in response to the AC current. The thermometer resistance isconstant, and the thermometer voltage is a pure sine wave, sinceV_(TH)=IR_(TH) and I is a pure sine wave. In this case there are nohigher harmonic signals. If the AC current is sufficiently large,however, the input power modulation at frequency 2ω will cause atemperature modulation, and therefore a resistance modulation, atfrequency 2ω, i.e., R_(TH)(t)=<R_(TH)>+ΔRe^(2iωt), where ΔR isproportional to ΔT. Since V_(TH)=IR_(TH) and I is a pure sine wave,V_(TH)=I₀e^(iωt)R_(TH)(t)=I₀<R_(TH)>e^(iωt)+I₀ΔRe^(3iωt). The firstharmonic voltage is thus proportional to the thermometer resistance, andtherefore to the temperature, while the third harmonic voltage isproportional to the temperature modulation, and therefore givesinformation about the heat capacity, as in the 2ω method.

Typically, the c component of V_(TH) is between 100 and 1000 timeslarger than the 3ω component, depending on the sample's particularthermal characteristics, the AC signal amplitude, and the geometry ofthe heater/thermometer 100. To analyze the voltage output from theheater/thermometer 100, a component in the electronic platform thatreceives the voltage output can lock in at frequency ω to detect thebasic sine waveform and at frequency 3ω to detect the third harmonic. Asexplained in FIGS. 13A and 13B, two separate lockin amplifiers 130, 132or a single lockin amplifier that can switch between the two frequenciescan be used. The advantage of using two separate lockin amplifierstuned, respectively, to the ω and 3ω frequencies 130, 132 is that boththe temperature and the heat capacity measurements can be conductedsimultaneously in real time, greatly increasing measurement speed andeliminating the waiting period needed for a single lockin amplifier tosettle after switching its frequency. A representative block diagramillustrating the components of a preferred sensor array and electronicplatform for the 3ω method is shown in FIG. 13B.

The 3ω method in its preferred embodiment requires additional signalprocessing equipment or methods in order to extract separately themodulation amplitudes at two separate frequencies. However, the 3ωmethod has a number of advantages over the 2ω method as well, and is thepreferred embodiment. In the 2ω method, the power modulation is producedby the heater 104, while the temperature modulation is sensed at thethermometer 102. The time constant t2 is the thus time required for heatto diffuse laterally across the membrane 94 from the heater 104 to thethermometer 102. While this time can be made fairly small, this stilllimits the frequency range to typically 5-50 Hz, and therefore placessome limits on the measurement speed.

In the 3ω method, the temperature modulation is both produced andmeasured by the thermometer; in this case, t2 is the time required forheat to diffuse vertically across the thickness of the membrane 94 andinto the thin film sample 90 rather than horizontally from the heater104 to the thermometer 102. Because the sample 90 and the sensor 12taken together are typically only a few microns thick, this time is muchshorter than the t2 associated with the 2ω method. This in turn permitsthe use of measuring frequencies in the kHz range, with a correspondingincrease in the possible temperature ramp rate and measurement speed. Inaddition, because the modulated power does not have to diffuse anydistance laterally across the membrane, there are no radiative losses asthe power travels from the modulation source to the modulation sensorsince they are one and the same.

Sample test results obtained using the 3ω method are shown in FIGS. 13Cthrough 13F. The samples are a film of low Tg solder glass, form Ferro,as detailed above. The configuration of the electronics platform for the3ω method is somewhat different than for the 2ω method, but once theconfiguration is completed, the measurement procedure is essentially thesame as described above with respect to the 2ω method. The heater rampvoltage is generated in the same way as in the 2ω method, but instead ofbeing summed with a modulation signal, it is simply buffered and sent tothe heater 104. The modulation signal contains a sinusoidal AC currentand is sent to the thermometer 102 instead of the DC current used in the2ω method. The AC current can be produced in many ways. For the examplediscussed here, the sinusoidal voltage output from a lockin amplifier'soscillator output is used as the input to a voltage-controlled currentsource, which is a simple op-amp circuit. The amplitude of themodulation current is typically several tens of mA in order to get anadequate third harmonic signal due to temperature modulation.

The thermometer 102 is connected in parallel to the differential inputsof two separate lockin amplifiers 130, 132. A ω lockin amplifier 130 isset to detect signals at the same frequency as the oscillator drivingthe AC current source, while a 3ω lockin amplifier 132 is set to detectsignals at the third harmonic of this frequency. The oscillator outputfrom the lockin 130 used to drive the AC current source is alsoconnected to the reference input of the second lockin 132, insuring thatboth lockins 130, 132 are synchronized and tuned to the correctreference frequency and phase. As noted above, the signal at 3ω istypically 100-1000 times smaller than the signal at o) (e.g., 10 μV vs.10 mV), so a much higher gain setting is used for the lockin which ismonitoring the third harmonic. Because the 3ω lockin 132 must reject themuch larger first harmonic signal, it must usually be used in “highdynamic reserve” mode, instead of “low noise” mode as is possible in the2ω method, in order to avoid overloading the inputs.

Once the measurement has been configured, the same measurement procedureused in the 2ω method can be used in the 3ω method. In this case,V_(th)(ω) corresponds to the resistance of the thermometer 102 and theaverage temperature; and V_(th)(3ω) corresponds to the temperaturemodulation and heat capacity, as explained earlier. The temperature iscalculated from V_(th)(ω) in the same way as described above for the 2ωmethod using <V_(th)>. However, the heat capacity is approximated asCp=V_(th)(ω)/V_(th)(3ω), which differs in form from the formulaCp=[<V_(th)>*V_(th)(2ω)] used with the 2ω method.

The reason is again related to the formula C_(p)=ΔP/2ωΔT, discussedearlier. In the 3ω method as described here, the modulation is driven bya sinusoidal current of fixed magnitude I_(th), and the power modulationin the thermometer ΔP is given by I_(th) ²R_(th), which is proportionalto R_(th) and therefore to V_(th)(ω). In the embodiment of the 2ω methoddescribed earlier, the modulation power to the heater was due to amodulation voltage of fixed amplitude V_(H). The modulation power isthen v_(H) ²/R_(H), and is inversely proportional to the heaterresistance.

It should be noted that both AC and DC power can be coupled into theheater 104 and/or thermometer 102 in either the 2ω or 3ω methods, andthe temperature and temperature modulation may be determined bymonitoring either the voltages on the sensors caused by known currents,or the currents caused to flow by known voltages. It should also benoted that other implementations of AC calorimetry in a sensor arrayformat are possible, without departing from the spirit of the invention.For example, two separate heaters and one thermometer can be used,wherein one heater provides a DC power input and the other heaterprovides an AC power input. Also, a single resistive element can be usedas both a heater and thermometer if the 3ω method is used and theresistive element is properly designed so that the temperature issubstantially uniform over the area of the thermometer. An example ofsuch a sensor design is shown in FIG. 13G. Although the sensor consistsof a single wire, with uniform current passing along its entire length,the voltage is only measured from a portion of the wire, which is in thecenter of the area being heated. A combined DC and AC current is used,and the voltage may have frequency components at all harmonics up to thethird. As in the previous description above, the temperature and heatcapacity may be obtained from the first and third harmonics,respectively. This sensor design has the advantage that both AC and DCpower are created uniformly across the entire sensor.

Further, the temperature of the sensor can be varied via an externalheating method, such as contact with a heated block or illumination byinfrared radiation, while the temperature and temperature modulation aremeasured electronically by the temperature sensor 102.

Although the preferred substrate for thermal analysis is a film having athickness comparable to the thickness of the sample, the use ofmodulation techniques, such as the 3ω method, also permits thermalanalysis of films on substrates that are much thicker than the sample.In such a case, the modulation frequency must be sufficiently high sothat the distance over which heat diffuses into the substrate during onemodulation cycle is comparable to or less than the sample thickness.This distance defines the effective sampling depth of the modulatedcalorimetry measurement, and so the heat capacity contributions from thesample and substrate will be comparable, even though the total heatcapacity of the substrate is much larger. The 3ω method is particularlyuseful in this case because it can access much higher measuringfrequencies than the 2ω method.

Experimental Example: Thermal Stability Analysis

The thermal analysis array structure explained above can also be used tomeasure the thermal stability of a material. Thermal stabilitymeasurements indicate how hot a material can get before it decomposes orvaporizes and how quickly decomposition takes place as its temperatureincreases. Thermal stability is particularly important when determiningwhether a particular material can withstand high temperatures withoutbreaking down or otherwise exhibiting volatile properties.

Thermal stability can be measured in several ways. FIG. 14 shows sampleresults of a glass transition and thermal decomposition of a polystyrenefilm using the sensor array of the present invention. The polystyrenewas obtained from Aldrich and used as obtained, which was catalog no.43,010-2 having a listed melt index of 8.5 and a molecular weight of230,000. The polymer sample was dissolved in toluene to create a 3%solution, which was manually pipetted onto the sensor. The sample wasallowed to air dry on the sensor and then placed in a chamber that wasevacuated for a measurement using the 3ω method, described above.Thermal stability measurements can be conducted via any of the signalmodulation methods described above. The measurement is conducted in anidentical manner as the heat capacity measurement, but the temperatureis increased until the material decomposes or otherwise gives up mass.When this occurs, the heat capacity drops sharply and the modulationamplitude increases sharply. This occurs because the same amount ofmodulated power is going into the heater/thermometer 100 and themembrane 94, but the sample has partially or largely disappeared, so themodulation becomes larger. Further, because the change in the materialis not reversible, the modulation will remain large even if thetemperature is lowered because of the material's irreversibly changedstate.

Heat capacity and thermal stability measurements conducted in thismanner are most appropriate for materials that do not liquefyexcessively when exposed to heat, such as high molecular weightpolymers, because materials having extremely low molecular weights maynot stay on the heater/thermometer 100 when heated and may tend to runto the edges of the sensor 12, leaving the heater/thermometer 100exposed. As a result, the exposed heater/thermometer 100 will give afalse indication of decomposition (e.g. a large increase in modulation),because much of the material is no longer on the sensor 12, when inreality the material has simply liquefied and flowed off theheater/thermometer 100. Thus, the thermal capacity measurementsdescribed above are more suitable for materials that tend to hold theirshape rather than low viscosity liquids. Thermal stability can also bemeasured with the present invention by heating the sample material onthe heater/thermometer 100 in a chamber until it bums and decomposes,then measuring the amount of gaseous fragments in the air as well as thefragments' mass and the air pressure within the chamber.

Dynamic Thermal Analysis

Dynamic thermal analysis may be a less quantitative technique foridentifying phase transitions. A sample is typically placed in a cell incontact with a heater block. One thermometer monitors the temperature ofthe sample, while another thermometer measures the temperature in areference cell or reference location. The difference in the temperaturesof the two thermometers is measured as the temperature of the heaterblock is steadily raised. The sample temperature tends to lag behind thereference cell temperature, in proportion to the heat capacity of thesample. Thus, phase transitions, such as glass transitions or meltingpoints, show up as kinks or bumps in the temperature vs. time curve.

A preferred structure for conducting dynamic thermal analysis in asensor array according to the invention is shown in FIG. 15A. Thestructure has a heater block 150 constructed from a block of materialhaving good thermal conductivity, such as copper or another metal. Thehigh thermal conductivity of the block material causes the heater block102 to have and maintain a uniform temperature throughout even while theheater power and temperature are varied.

The preferred structure also includes a glass plate 152 that is placedon top of the metal block. Glass is the preferred material for thickersubstrates because of its relatively low cost, rigidity, and low thermalconductivity. A plurality of temperature sensors 154, are printed on thetop surface of the glass plate 152 in any desired array configurationusing any known method, such as lithography. Because glass has very poorthermal conductivity, there will be a relatively large differencebetween the top and the bottom surfaces of the glass plate 152.

For clarity, the following discussion will describe characterization ofa single material, but a library of materials can be simultaneouslyand/or selectively characterized on the sensor array. The main principlebehind dynamic thermal analysis is that the temperature drop across thethickness of the glass plate or between two predetermined points on asurface of the glass plate is proportional to the heat flow through theglass into the sample. Although this ignores the heat flow that isabsorbed by the glass to raise its temperature, this heat absorption isthe same at all locations on the sensor array and can effectively bedisregarded. For materials characterization, as illustrated in FIG. 15A,a sample material is placed on a sensor and the temperature of theheater block T0 is increased to supply heat through the glass plate 152to a sample 156. In this particular example, the temperature increase inthe heater block 150 will create a temperature difference ΔTij acrossthe thickness of the glass 152, and the heat will eventually conductthrough the glass to heat the sample up to a temperature Tij. Thus, thetemperature difference across the glass plate ΔTij=Tij−T0.Alternatively, the temperature difference can be measured between apoint on the glass plate 152 containing the sample and a reference pointon the glass plate 152, which reference point may contain a sample thatis known to not have any phase transitions in the temperature range ofinterest.

The sensors 154 on the glass plate 152 measure the temperature andtemperature increase rate of each sample. If the temperature of thesample 156 is rising at 1 degree per second, for example, there must bea certain amount of heat flowing through the glass 152 to the sample156. When the temperature of the heater block 150 is ramped upward, acertain amount of heat flow J is required to increase the sample'stemperature at the same rate. If there is not enough heat supplied tothe sample 156 to raise its temperature, the temperature of the sample156 increases mores slowly than the heater block 150, increasing thetemperature difference ΔTij between the top and bottom surfaces of theglass 152. As the temperature difference increases, more heat flowsthrough the glass 152. For each material, there is a specific value ofΔTij at which the heat flow through the glass 152 is the correct, steadystate amount for raising the temperature of the material sample. Becauseeach material has different thermal characteristics, the heatertemperatures at which this steady state condition occurs, and thus theΔTij value, will be different for different materials.

The temperature difference ΔTij corresponds qualitatively to the heatcapacity of the sample 156 because some materials require a greater heatinput to raise its temperature a certain amount and therefore causes ahigher value for ΔTij. As a result, a large ΔTij correspondsqualitatively with a higher heat capacity material, while a lower ΔTijcorresponds to a lower heat capacity material. More importantly, thelarge changes in the heat capacity, which occur at phase transitions,will show up as kinks or bumps in the temperature vs. time data for agiven sensor. For example, the temperature difference ΔTij between thetop and bottom surfaces of the glass plate 152 increases sharply at amelting point because large increases in the heat input result in littleor no change in the sample material's temperature; the temperatureincrease in the sample material lags behind the temperature increase inthe heater block 150 by a much larger amount than at a point away fromthe melting point of the sample 156. After melting is complete, ΔTij mayreturn to a lower value.

The structure for dynamic thermal analysis is particularly suitable fortesting materials that cannot dissolve easily in a liquid and form athin film on the sensor when the liquid evaporates, such as highlycrystalline polyethylene samples. For dynamic thermal analysis, asexplained above, the sample material can be simply dabbed onto eachsensor without having to form a thin film, e.g., from a slurry, gel, orpowder. Further, the thermal characteristics of the glass plate 152 inthe present embodiment do not adversely affect the thermalcharacterization procedure if the dimensions of the material sample andthe glass plate's thickness are on the same order of magnitude.

FIG. 15B is a representative block diagram of a materialscharacterization apparatus that is designed for dynamic thermalanalysis. As explained above, an insulating substrate, such as a glassplate, has a plurality of thermometers 154 disposed on its surface andsits on top of a metal block heater. The temperature of the metal blockheater is increased, and the electronic platform monitors thetemperature of the block with one or more thermometers that are incontact with the block.

Because the entire sensor array structure is heated simultaneously inthis particular example, all of the samples on the sensor array must bemeasured simultaneously or via rapid repeated scanning. Therefore, thepreferred electronic link between the sensor array and the electronicplatform will include multiple channels for monitoring the sensoroperation, preferably one channel per sensor, for maximum speed.Alternatively, the electronic platform rapidly scans through all of thesensors via the multiplexer to measure each sample's temperature (bymeasuring the resistance in each thermometer). The temperaturedifference ΔTij can be calculated by the computer or processor, ifdesired, to generate the thermal characterization data and/or plot. Thereference temperature can be the temperature of the heater block 102, orthe temperature of a sensor that does not carry a sample or that carriesa sample having no phase transitions over the temperature range beingstudied.

Experimental Example: Dielectric Spectroscopy

The sensor array of the present invention is not limited only toconducting thermal analysis. As illustrated in FIGS. 16A through 16D,for example, the invention can also characterize electrical properties,including but not limited to the complex dielectric constants ofmaterials.

The basic principles behind dielectric spectroscopy are now brieflydiscussed. To measure the dielectric constant of a material, thematerial is typically placed in between two metal plates that have anelectric field in between them going from a positive charge to anegative charge. If the molecules of the material in between the twometal plates are more asymmetric, they usually have a greater tendencyto polarize in response to the electric field, and the molecules willrotate so that they align with the electric field. The molecularrealignment of the material creates its own electric field responsive tothe electric field imposed on the material and tends to cancel out atleast part of the imposed electric field. Materials having strongerdipole characteristics (and therefore a greater dielectric constant)will create a stronger responsive electric field and will thereforecancel out a greater portion of the imposed electric field.

The overall electric field reduction can be measured by monitoring thecharge Q required to create a voltage V between the two metal plates.When the material to be tested is placed between the metal plates, anadditional charge (∈−1)Q may flow onto the plates to maintain thevoltage V, wherein ∈ is the dielectric constant of the material. As canbe seen from the equation, a material with a larger dielectric constantwill require more charge to achieve a given voltage drop across themetal plates. In short, the plates and the material together form acapacitor, and changes in the capacitance reflect changes in thedielectric constant.

The dielectric constant provides information about the physicalcharacteristics of the material being tested at the microscopic level.Some molecules whose positive and negative charges are at the center ofeach atom in the molecule will exhibit dielectric properties when placedin the electric field because the electric field will slightly displacethe nuclei of the atoms in the molecules, creating a positive charge atone end of molecule and a negative charge at the other end. Materialsthat exhibit greater dielectric properties, however, often havemolecules that are asymmetrically charged to begin with. When thematerial is placed in the electric field, the molecules simply rotateand align themselves with the electric field.

Monitoring the dielectric properties of materials over time is aneffective way to detect, for example, curing or cross-linking of glues,thermosets, epoxies, and similar adhesive materials. FIG. 16Billustrates an example where the dielectric properties of a 5-minuteepoxy are monitored over time using the sensors described below. In atypical epoxy curing reaction, the molecules in the liquid resininitially move and rotate relatively freely, allowing them to orient inresponse to an imposed electric field. As the molecules begin tocross-link (e.g., thereby hardening the epoxy or glue), they are lessable to align themselves in response to the electric field, decreasingthe dielectric constant of the material and thereby decreasing thesensor's capacitance. After the epoxy is completely cured, the moleculesare not able to realign themselves, dropping the dielectric constant ofthe material, and therefore the capacitance of the sensor down evenfurther. Thus, monitoring changes in the dielectric constant of amaterial over time can provide valuable information about the speed andnature of chemical reactions, such as the epoxy curing reactiondescribed above.

FIGS. 16A, 16C, 16D and 16E explain the preferred sensor geometry andapparatus structure that can be used for dielectric spectroscopy in thesensor array of the present invention. For simplicity, the structure andoperation of only one sensor is discussed, but, like the otherexperimental examples, the preferred method and apparatus for conductingtesting involves using a plurality of sensors disposed on a sensor arrayand coupled with an electronic platform, as represented in FIG. 16E. Themost common technique for measuring the dielectric constant of amaterial is, as noted above, forming a capacitor with the material to betested in between two plates. Forming a sandwich-type capacitor andobtaining measurements from such a capacitor, however, is often acumbersome operation, especially when used with liquid samples.Furthermore, the geometry of the capacitor needs to be well defined; theuser should know the exact thickness of the capacitor layers, positionthe plates, and maintain these dimensions throughout the testing.

As shown in FIGS. 16C and 16D, a preferred sensor structure fordielectric measurement according to the present invention is a planarcapacitor having interdigitated electrodes 160. The interdigitatedelectrodes look somewhat like two interlocking combs where the “teeth”162 do not touch each other. Note that because the thermalcharacteristics of the substrate 164 are not a concern when measuringelectrical properties, the substrate supporting the electrodes 160 canhave any thickness (i.e., it does not have to be a thin membrane).However, it is desirable that the substrate 164 should have lowdielectric losses under the desired measurement conditions and notexhibit any phase transitions or other unusual behavior. Thus, theelectrodes 160 themselves can be printed on glass sheet, quartz,sapphire, or any other desired inert substrate material.

The advantage of the interdigitated electrodes is that the materialsample's dimensions do not affect the output of the sensor because thecapacitors formed by the wires of the interdigitated electrodes 160 areso small; as long as the thickness of the material placed on theelectrode 160 is a few times larger than the spacing between theelectrode wires, the thickness of the material sample is no longerimportant because the electric field is virtually zero at a distancethat is several times the spacing between the wires 162. For example, ifthe spacing between wires 162 in the electrodes is 5 microns, theelectric field is reduced roughly by a factor of 10 for every 10 μm ofdistance away from the surface. The wire spacing is preferably kept assmall as possible so that the capacitance can be kept large enough tomeasure easily. More particularly, the capacitance obtained from a givensensor will be in the range of L²/D (in picofarads pF), where L is thelength of one side of a square sensor and D is the spacing between thewires, both in units of centimeters. For this example experiment theelectrode 160 dimensions for use in the sensor array of the presentinvention was a 2 millimeter square sensor with a 5 micron wire spacing,which will give capacitance readings of around 10-15 pF. However, theelectrodes 130 can any have dimensions to obtain a capacitance rangemeeting the user's own specifications.

For example, the sensor array used in the experiment shown in FIG. 16Bwas fabricated from 1000 Å Cr metal on a 5″ square glass substrate usinga standard photomask blank as a starting substrate. The startingsubstrate is preferably purchased pre-coated with the metal and aphotoresist. The photoresist was patterned by contact printing from amaster photomask, and the exposed Cr metal was etched away chemically.The resulting interdigitated electrodes 130 cover a 2 mm square andcontain lines and spaces of 5 μm.

FIG. 16E is a simplified block diagram representing a materialscharacterization system having a sensor array that is designed formeasuring dielectric properties. Like the other embodiments describedabove, the sensor array is controlled by an electronic platform via amultiplexer that directs electronic signals to and from selectedsensors. The electronic platform can measure the complex impedanceacross each capacitor to determine the capacitance, resistance andcomplex dielectric constant of the materials on each sensor. Forexample, the capacitance of a sensor can be measured in less than 0.1seconds using a conventional capacitance/resistance meter or impedanceanalyzer. The multiplexer can scan the electrodes 160 in any order andany combination rapidly, as explained in previous examples.Alternatively, a separate drive circuit can be provided for each sensorso that the sensors can be measured simultaneously. The capacitance andlosses due to the various interconnect circuitry, including wires,signal routing means 129, etc., can be measured with the sensor array 10removed from the apparatus. Subsequent measurements with a sensor array10 in place can then be corrected to separate the impedance of theelectrodes 160 from the impedance due to the interconnects.

Because dielectric spectroscopy does not necessarily involve measuringthe thermal properties of the material, monitoring the materialtemperature is not necessary if measuring the dielectric constant alone.However, the interdigitated electrode structure can be combined with,for example, a resistance thermometer 166. This combined structure canmonitor changes in the dielectric constant during a chemical reactionwhile simultaneously monitoring thermal events such as exotherms. Thecombined electrode/thermometer structure preferably has the thermometerplaced in the center of the electrode to provide the most accuratetemperature reading. By conducting the dielectric and thermalmeasurements simultaneously, more information is made available from asingle experiment. In addition, the glass transition of the cured resincan be measured by operating the system in Dynamic Thermal Analysismodes as described above.

More specifically, the scans shown in FIG. 16B were obtained by couplingselected sensors to an SRS 560 LCR meter (inductance/capacitanceresistance meter) operated at a 1 kHz frequency. Although one preferredoperation mode includes repeated measuring the capacitances of multiplesensors in the array 10 during a single experiment, the data shown inFIG. 16B was acquired one sample at a time. The LCR meter was coupled toa selected sensor's contact pads 14 via two wires attached tomicropositioners. Once the sensor was contacted, a fluid sample wasapplied directly to the sensor, and measurements were recorded manuallyonce per minute, for a total time of ten minutes. The capacitance of theleads, before connecting them to a sensor, was approximately 1 pF. Thecapacitance of a bare sensor with the leads was approximately 15-20 pF.The capacitance of a sensor with one of the epoxy components placed ontop of it was typically 30-40 pF immediately following application ofthe sample.

The epoxy used in the specific example shown in FIG. 16B is Devcon5-minute epoxy. In the experiments conducted on the individual epoxycomponents, denoted A and B in the figure, fresh samples of thecomponents were removed from the storage tube immediately before beingapplied to the sensor. When a mixture of A and B was tested, the twocomponents were removed from their tubes and mixed for approximately 30seconds before being applied to the selected sensor. A large reductionof the sensor capacitance can be seen for the sample of the mixed epoxy,corresponding to setting, while the capacitance for the individualcomponents A and B change by much smaller amounts.

Determining the dielectric properties of materials in and of themselvescan also be important. For example, integrated circuits often includesdielectric layers separating multiple wires from each other to minimizeor eliminate cross-talk, and it has been found that lower dielectricconstant materials, which do not polarize easily, allow signals topropagate more quickly. Thus, conducting dielectric spectroscopyaccording to the claimed invention allows rapid screening of manymaterials to find materials that have the optimum dielectric properties.

Experimental Example: Surface Launched Acoustic Wave Sensors

FIGS. 17A and 17B show an example of a surface launched acoustic wavesensor 170 for measuring material properties such as viscosity, density,elasticity, and capacitance. An electrode in the surface launchedacoustic wave sensor may also have interdigitated fingers 172, in thiscase for launching and measuring transmission of acoustic energy.Further, like the examples shown in FIGS. 16C and 16D and describedabove, the interdigitated structure of the sensor electrodes in FIGS.17A and 17B can measure the dielectric constant and the conductivity ofthe material, if desired.

In this example, surface launched acoustic wave sensors can befabricated on thin silicon-nitride or etched silicon membranes 174similar to those described above. A piezoelectric material 176, such aszinc oxide, is then deposited as a thin layer on top of the membrane toproduce an acoustic wave sensing device. The physical dimensions of theelectrode, such as its thickness, size, and configuration, can beadjusted so that the electrode operates in, for example, a surfaceacoustic wave (SAW) resonance mode, a thickness shear mode (TSM), aflexural plate wave (FPW) resonance mode, or other resonance mode. Whenthe electrode acts as a resonator, its resonating response is affectedby, for example, the sample's viscosity and density. U.S. applicationSer. No. 09/133,171 to Matsiev et al, filed Aug. 12, 1998, describesmechanical resonators in more detail and is incorporated by referenceherein.

Thus, because the surface launched acoustic wave device shown in FIGS.17A and 177B can serve as both a mechanical resonator and as a sensorfor characterizing other material properties, such as the dielectricconstant, multiple devices can be arranged in a sensor array format toscreen material properties. The versatility of the surface launchedacoustic wave device and other mechanical resonators make it a goodchoice for observing multiple materials as they undergo a chemical orphysical process involving changes in viscosity, density, conductivity,molecular weight, or chemical concentration.

Further, the mechanical resonator can be used to measure weight or forcebecause of its responsiveness to mechanical loading. When surfacelaunched acoustic wave sensors are arranged in an array format, thesensor array can be used to weigh simultaneously multiple samples ofpowders or liquids, each sensor acting as a separate scale. As notedabove, these mass measurements can be conducted simultaneously withviscosity, conductivity, and dielectric constant measurements due to theinterdigitated structure of the sensor electrode. Electroplating orsolution deposition could also be measured using the arrayed mechanicalresonators by correlating the resonator response to mass loading.

The mechanical resonator structure shown in FIGS. 17A and 17B can alsobe used for magnetic material characterization. More particularly, themass loading effect of the resonator can be used to measure a samplematerial's response to an external magnetic field. In this application,the resonators in the array are coated with the test material ormaterials, and the sensor array is placed in a magnetic field. Anymagnetic response of the material to the magnetic field would appear asa change in the mass loading experienced by the resonator. This massloading change damps the resonance signal from the resonator, and theamount of damping can be correlated with the material's response to theapplied field. Alternatively, a mechanical actuator can be used in thesame manner as the mechanical resonator, and characterization would beconducted by measuring the amount of displacement in the actuator.

Experimental Example: Electrical Transport Properties

Yet another set of material properties that can be measured using thematerials characterization system of the present invention are theelectrical transport properties of materials: electrical resistance,Hall effect resistance, magnetoresistance, and current-voltage curvesshowing non-linear features such as breakdown voltages and criticalcurrents. As explained above, the “plug-and-play” format of theinvention may only requires the user to change the sensor array, not theentire machine or any hardware, to measure a different materialproperty, depending on the embodiment being practiced. The changes mayoccur at the sensor level; the electronic platform and multiplexer canremain generally the same regardless of the specific materialcharacteristic to be tested. Minor variations in the electronichardware, such as amplifiers, voltmeters, capacitance meters and thelike may be needed to conduct the measurements, but these modificationscan be external to the sensor array and can be conducted in the flexibleelectronic platform. The following discussion will focus on the specificsensor structure that is used to measure electrical transportproperties; the connections between the sensor array, the multiplexer,and the electronic platform, as well as their operations, are similar tothe connections and operations described above.

FIG. 18A show a preferred sensor structure that can measure theelectrical transport properties of a material. Like the above examples,a plurality of the sensors are disposed in an array format to measurethese properties for a materials library quickly. As is known in theart, resistivity is an intrinsic property that does not depend on thedimensions of the material, and resistance equals the resistivity p ofthe material times the length of a material sample L divided by thematerial sample's cross-sectional area A (R=ρL/A). The Hall coefficient,as is also known in the art, indicates the number of electrons or holesin a material per unit volume and indicates the sign of the chargecarriers.

Measuring these two characteristics according to the present inventionis relatively simple. The materials to be tested are formed into bars180 having known dimensions, and the sensors used to test the materialare equipped with six leads 182 that preferably contact the bar ofmaterial at both ends and in the middle, as shown in FIG. 18A. The bars180 themselves can be formed by depositing the library elements througha mask onto the leads 182, or by depositing the materials on thesubstrate first using a mask and then printing the leads 182 on top ofthe bars 180, again using a mask. In some cases, the bar 180 should besintered or annealed after deposition, so the anticipated effects of thesintering/annealing process on the contacts should also be consideredwhen selecting a depositing order. Like previous embodiments, thecontact pads in this embodiment provide the connection between thesensor array and the electronic platform that sends and reads signals toand from the individual sensors.

To obtain a material's resistance, an AC or DC current is simply passedthrough the bar 180 and the AC or DC voltage across the bar 180 ismeasured using leads EC or FD, without placing the sensor array in amagnetic field. To obtain a material's Hall coefficient andmagnetoresistance, the sensor array should be placed in a magnetic fieldB that points perpendicular to the substrate. The magnetic field B canbe generated in a variety of ways. For example, a large permanent magnetor electromagnet 184 can be used to generate a magnetic field that isperpendicular to the substrate over the entire sensor array, as shown inFIG. 18B. Any non-uniformity in the magnetic field B can be detectedbefore conducting the materials characterization, by using an array ofidentical, calibrated Hall effect sensors, and this non-uniformity canbe taken into account in any subsequent analysis of the data obtainedfrom the sensor array with samples. Alternatively, as shown in FIG. 18C,an array of permanent magnets or electromagnets 186 having the samearray format as the sensor array can be used in place of the singlemagnet. The pole portions of the magnet array are preferably placedclose to the individual samples and sensors in the sensor array. As forthe single magnet, the magnet array can be calibrated with an array ofHall effect sensors to detect any non-uniformities or variations in thefield strengths produced by the individual magnets so that thesevariations can be taken into account in subsequent analysis of the datafrom the sensor array.

During testing, a current is sent through the bar 180 using contacts Aand B. The material's resistance in a magnetic field, known asmagnetoresistance, can be measured in the same manner as resistanceexcept the sensor array is exposed to a magnetic field so that thesensor can measure any changes in resistance in response to the magneticfield. The Hall voltage is obtained by measuring the voltage across thewidth of the bar, at contacts CD or EF, and the Hall resistance is givenby:

V _(H) =IR _(H) =I(B/nec)

As can be seen from the equation, the Hall voltage for a given magneticfield strength corresponds to the charge carrier density (n) and thesign of the carriers (+e or −e) for the material being tested. As iswell known in the art, the Hall voltage results from the forces onmoving charge carriers in a magnetic field. This force, which isperpendicular to the direction of motion as well as the field direction,causes positive and negative charges to build up on opposing edges ofthe sample until the resulting electrical force on the moving chargecarriers exactly cancels the magnetic force. This condition can be usedto derive the above equation for the Hall resistance.

Experimental Example: Thermoelectric Material Properties

Yet another group of properties that can be measured using the sensorarray of the present invention are two characteristics of materials thatpertain to their desirability for use in thermoelectric cooling devices:thermopower and thermal conductivity. Thermopower will be discussedfirst.

When a temperature gradient is imposed on a material under open circuitconditions, an electric field occurs due to the diffusion of chargecarriers in the temperature gradient. In equilibrium, the force on thecharge carriers due to the electric field is just sufficient tocounteract their tendency to diffuse in the temperature gradient. Theratio between the temperature drop and the voltage drop across a sampleis known as the thermopower, S=ΔV/ΔT, and is typically measured in unitsof μV/K. The thermopower is a fundamental physical property of anelectronic material that can provide information about a materialselectronic structure and other characteristics. In addition, thethermopower is a key physical parameter for materials which are used asthermoelectric cooling devices. A large thermopower value is a desirableproperty for a material in cooling device applications. To search forimproved thermoelectric materials using combinatorial chemistrytechniques to synthesize libraries of thin films of candidate materials,it is desirable and necessary to be able to measure rapidly thethermopower of many materials.

The thermopower, S, can be measured using the sensor design explainedabove and shown in FIG. 19A by measuring the voltage drop ΔV across abar sample 190 for a known temperature difference ΔT along the sample190. This can be conducted in a variety of ways. In one embodiment, asillustrated in FIG. 19B, a temperature gradient is imposed along theentire sensor array 10 by contacting two opposing edges 191, 192 of thearray with metal blocks 194, 196 whose temperatures are controlled andmeasured. If the substrate has high thermal conductivity, such assilicon, then heat losses to radiation and convection will be relativelyminor compared to the heat conduction along the substrate, and a fairlyuniform temperature gradient will be produced. The gradient may beapproximated as the total temperature drop divided by the width of thearray, and the temperature drop across an individual sample will be thegradient times the length of the sample. In other words,ΔT_(sample)=ΔT_(array) * (L_(sample)/L_(array)). More preciseinformation about the temperature drop across each sample may beobtained by including two temperature sensors next to each sample withinthe sensor array 10, one near each end.

The above example ignores heat losses through the electrical contacts tothe sensor array, which may cause the temperature profile to deviatefrom the preferred linear gradient form or cause most of the temperaturedrop to occur over a relatively small distance near the edge of thearray instead of evenly across the entire array. An alternativeembodiment which is not subject to this problem is shown in FIG. 19C. Inthis embodiment, a chain of heating/cooling elements 198, such asthermoelectric heat pumps, is used to impose a temperature drop acrosseach row in the sensor array, by means of blocks of metal or otherthermally conductive material that contacts both the heating/coolingelements 198 and the substrate. The elements 198 preferably alternatedirection so that all of the samples in the array 190 are at the sameaverage temperature. The structures that produce the temperaturegradient on the array may be integrated into the compression plate 44,shown in FIG. 4, used to apply pressure on the sensor array against thecontacts to the circuit board.

In yet another embodiment, the temperature gradient can be produced byresistive heating elements that are part of the sensor array itselfrather an external heating fixture. This structure is most easilyaccomplished if the substrate has low thermal conductance, either via alow thermal conductivity material (e.g., glass) or via a thin filmsubstrate (e.g., silicon nitride). A large number of configurations arepossible; ideally, temperature sensors are placed at both ends of eachsample and a resistive heating element is placed near one end of thesample. In addition, at least two electrical connections are at the endsof the sample for measuring the thermoelectric voltage.

Experimental Example: Thermopower (Seebeck Coefficient) Measurements

In the embodiment of thermopower measurements proposed in co-pendingU.S. application Ser. Nos. 09/210,086; 09/210,428; and 09/210,485, atemperature gradient is imposed on the substrate and samples by placingthe substrate in contact with two or more temperature controlled blocks(domestic application, FIG. 19C). This method has the advantage ofaffording good control over the magnitude and uniformity of thetemperature gradients, but requires the use of additional apparatusbeyond that included in materials characterization system of the presentinvention.

In order to demonstrate the feasibility of making thermopowermeasurements in an array format without the need for additionalapparatus, a sensor was designed which included a resistive heater atone end of the sample, in addition to leads for current injection,longitudinal voltage measurement (resistance), and transverse voltagemeasurement (Hall effect). This sensor design is shown in FIG. 22.Arrays of these sensors were fabricated using 0.2 μm sputtered nickelmetallization, on a substrate consisting of a silicon wafer with 0.5 μmof thermally grown silicon oxide electrical insulation. The combinedsystem of a material sample and the nickel leads forms a two-junctionthermocouple. The net voltage across the thermocouple is given byv_(th)=(S_(x)−S_(Ni))ΔT=SΔT, where S_(x) is the thermopower of thesample, S_(Ni) is the thermopower of the nickel leads, and ΔT is thetemperature drop due to the power generated by the heater.

When a voltage is applied to the heater, power is generated primarily inthe narrow “hairpin” heater wire. The end of the sample close to theheater will be warmer than the opposite end, and a thermal voltage willbe generated, which can be measured by coupling a pair of voltage leadsto a sensitive DC voltmeter. Because the silicon substrate is roughly1000 times thicker than the sample (typically 0.5 mm vs. 0.2 microns)and has high thermal conductivity (of order 1 W/cm° K.), almost all ofthe heat generated will flow through the substrate, not the sample, andthe temperature distribution for a given power level will therefore beessentially independent of the properties of the sample. Therefore, thetemperature drop across a sample is determined primarily by the heaterpower level, independent of the thermal conductivity of the sample.

Thus, for a given power level, the thermal voltages generated indifferent samples in an array will be proportional to the totalthermopower of the thermocouple formed by the sample and the nickelleads. If a sample with known thermopower is included in a materialslibrary, then the relationship between temperature and heater power canbe determined, and the data from other samples converted to absolutethermopower. Thus, although the detailed temperature distribution forthis sensor design has not been calculated, this is not necessary toobtain meaningful thermopower measurements.

A 64-element test library was synthesized on an 8×8 sensor array. Eachrow contained a binary composition gradient from Bi to Sb, and all 8rows were identical. The library was synthesized by sputteringalternating layers of Bi and Sb, each with a maximum thickness of 5 nmand with a linear thickness gradient across the library defined by amoving shutter, until a 200 nm film was built up over the entire array.The electronics used to measure the thermopower are shown in FIG. 23. Avoltage generated by a digital-to-analog converter is buffered by aunity gain inverting amplifier and then applied to the heater. Thethermal voltage v_(th) from the sample is low-pass filtered (cutofffrequency=1 kHz) and amplified (G=10⁴) by a Stanford SRS580 low noisepreamplifier, before being recorded by an analog-to-digital converter.For each sample, the heater drive voltage V_(H) is varied in uniformsteps from V_(min) to V_(max), where V_(min)=−V_(max), and the thermalvoltage v_(th) is measured for each value of V_(H). The power generatedby the heater is given by P=V_(H) ²/R_(H) and to a first approximationthe temperature drop across the sample will be proportional to P.Therefore, we expect the thermal voltage, v_(th)=bV_(H) ², and theconstant b should be proportional to the thermopower S (which ismeasured in μV/° K.). Again, the relationship between b and S, thethermopower, can be determined by measuring a sample with knownthermopower, and this relationship can be used to convert b to S for theunknown samples.

FIGS. 24A-C show a complete set of raw data for the BiSb test library.For each sample, V_(th) is plotted against V_(H) and is seen to describea parabola, v_(th)=a+bV_(H) ². The offset v_(th)=a at V_(H)=0 is due toan input offset of the preamplifier. It can be seen from the data thatthe coefficient b varies widely over the BiSb library, in both magnitudeand sign, but is essentially constant for a given composition. Thecoefficient b is plotted in FIG. 24C for the entire library. All of theobserved trends are consistent with the data reported in FIG. 38 of thepaper “Electric Transport Quantities of Bismuth-Antimony Alloys”, by J.Neisecke and G. Schneider, (Zeitschrift fur Naturforschung A, vol. 26,pp 1309-1315, 1971), as can be seen in FIG. 25. The sensor data for allsamples of a given composition (each column) have been averaged, andcorrections have been applied to account for the thermopower of thenickel leads. The data have been normalized to −65 μV/° K. at 100 atomic% Bi.

The sensor array structure for measuring thermal conductivity will nowbe discussed. Like thermopower, thermal conductivity is important fordetermining how efficient a given material will be for use inthermoelectric cooling devices. An ideal material in a cooling deviceapplication will have low thermal conductivity in conjunction with lowelectrical resistance to minimize heat leakage in the device and createa large temperature difference across the device with minimum energyconsumption and heat dissipation.

FIGS. 20A and 20B show a preferred sensor structure for measuring thethermal conductivity of materials. As in the previous experimentalexamples explained above, the description will focus on the structure ofa single sensor, but it is understood that multiple sensors are used inthe present invention in an array format, and that sensors measuringdifferent properties can be included on the same sensor array. Also,analysis of thermal conductivity may be useful in materials researchcontexts other than the search for new thermoelectric materials.

The preferred thermal conductivity measurement method is viavapor-deposited films, on the order of half-micron thick, on membranes,similar to the structure used for heat capacity measurements. Othermethods may also be used to deposit thin film samples, such asevaporation from a solution or suspension. As in heat capacitymeasurements, thermal conductivity measurements preferably minimize theeffects of the substrate's thermal characteristics on the overallmeasurement results. FIGS. 20A and 20B illustrate a preferred sensorstructure 200 for measuring thermal conductivity. As can be seen in FIG.20A, the sensor structure 200 for thermal conductivity measurements canbe of similar construction and materials as the structure used in heatcapacity measurements, such as a silicon-nitride membrane, so that thethermal characteristics of the material sample can be easily detectedand separated from the thermal characteristics of the substrate on whichthe sample sits. Thus, the details of the structure will not be repeatedhere.

Referring to FIG. 20B, a desired sensor pattern is printed via any knownmethod, such as lithography, on the membrane 202 surface opposite thesurface on which the material sample 204 will be deposited. Thisprevents a short-circuit from forming when characterizing electricallyconductive materials, such as metals. In this example, the sensorincludes two wires 206, 208. The specific geometry of the sensor shouldbe optimized so that the temperature is substantially uniform along theportion 205 of the sensor 200 over which the temperature will bemeasured on the membrane 202 (e.g., the “active” portion). To accomplishthis, the membranes 202 on the sensor array should be made relativelylong and narrow to insure that heat flow in the active portion ispredominantly between a second (heater) wire 208 and the nearbysubstrate 210, which contains a first wire 206, i.e., across the widthof the membrane 202 (perpendicular to the heater wire 206) and not alongthe length of the wire 208.

As noted above, a preferred sensor design includes two parallel wires206, 208 having a known width and spaced a known distance apart. Branchleads 206 a, 208 a extend from each parallel wire 206, 208 and arespaced a known distance apart for conducting voltage measurements V1 andV2 along the parallel wires. In this embodiment, the first wire 206 isused as a thermometer and the second wire 208, which is on the membrane202, is used as both a heater and a thermometer. As in previouslydescribed structures, the temperature is monitored by measuring the ACor DC voltage and current of the sensor and calculating the resistance,which varies linearly with respect to temperature.

In a preferred structure, the first wire 206 is disposed on the solidsilicon substrate 210, near the edge of the silicon nitride membranewindow 202, while the second wire 208 is disposed on the membraneportion 202 of the substrate. The silicon in the substrate 210 acts as alarge heat sink to prevent the temperature detected by the second wire208 from rising in response to the heat generated by the first wire. Ifthe width of the membrane 202 is kept small (e.g., less than 1 mm wideand preferably less than 100 μm wide), heat losses due to radiation maybe neglected in comparison to the total heat flow through the membraneand sample, and if the thermal conductivity measurements are conductedin a vacuum, heat losses to the atmosphere due to conduction andconvection may be neglected. Virtually all of the heat produced by thefirst wire 206 conducts through the membrane 202 and the sample 204, ina direction perpendicular to the wires 206, 208.

The theory behind thermal conductivity measurements will now bedescribed with respect to the structure shown in FIGS. 20A and 20B. Asnoted above, thermal conductivity is a measure of how easily heattravels through a material when a temperature difference T2−T1 isimposed on a material sample. When a temperature difference ΔT=T2−T1 isimposed across a material sample, such as a bar sample, heat will flowfrom the warmer end of the sample to the cooler end. This heat flow J(in watts) is equal to the thermal conductance K multiplied by thetemperature difference ΔT. In other words, the amount of heat flowthrough the sample is proportional to the temperature difference acrossthe sample. The specific proportionality constant depends on both thesample's geometry and the thermal conductivity κ of the material,K=κ(A/L) where A is the cross-sectional area of the bar in the directionperpendicular to the heat flow, and L is the length. In this sensor,L=the distance from wire to the edge of membrane/substrate, andA=(thickness of membrane/sample)×(distance between branch leads).

Referring back to the sensor structure shown in FIGS. 20A and 20B, thesecond wire 208, which is used as both the heater and the thermometer,carries a relatively large current 12 to generate a known power P forheating the sample and also measure the temperature of the wire; whilethe first wire 206 receives a small current I1 to conduct a temperaturereading. The large current I2 should be large enough to causesignificant self-heating in the portion of the sample around the firstwire 206, on the order of 5 to 10 degrees C. The small current I1 ispreferably the smallest amount of current necessary to measureaccurately the resistance of the second wire; it should not be largeenough to heat the sample to any significant degree. Even though thesmall current I1 may cause the sample's temperature to rise a smallamount, on the order of a tenth or a hundredth of a degree, thistemperature change is negligible relative to the self-heating occurringon the portion of the sample on the membrane and can therefore beignored. Further, as noted above, the silicon substrate 210 acts as alarge heat sink, keeping the temperature of the sample in that areauniform and preventing the temperature of the first wire 206 from risingalong with the temperature of the second wire 208.

To measure the temperature difference ΔT=T2−T1, the electronic platformonly has to monitor the resistance changes in the two wires 206, 208.The power I₂V₂ generated by the heater, which is equal to the total heatflux, and is input into the sample via the first wire, is known frommeasurements of I and V. Because the geometry of the sample is alsoknown, the thermal conductivity of the material can be obtained from thetemperature difference. Note that the thermal conductivity of themembrane 202 still has to be subtracted from the thermal conductivitymeasurement obtained from the combined membrane and sample, to obtainthe thermal conductivity of the material, but the membrane's thermalconductivity is easily determined by sending current through the sensorwithout any material on it, i.e., before deposition of the materialsample.

Experimental Example: Thermal Conductance/thermal ConductivityMeasurements

FIG. 26 shows the design and principal of operation of a thermalconductivity sensor which was fabricated and tested in an array format.The silicon nitride membrane in the tested devices was 0.4 μm thick, andthe metallization was 0.2 μm thick platinum. The width of the narrowestlines in the sensor is 0.001″ (approximately 25 μm), and the distancefrom the wire to the edge of the membrane is 0.01″. The wire on themembrane is used as both a resistive heater and a temperature sensor. Acurrent passed through the wire generates power P=IV=I²R. The sensor isdesigned so that almost all of this power is dissipated via heat flowthrough the membrane towards the nearest edge of the silicon wafer. Fromthe heat conduction equation J=κ(dT/dx) (where J=energy flux in W/cm²and κ=thermal conductivity in W/cm° K.), the relationship between thepower P and the temperature difference ΔT between the wire and thesubstrate is given by P=κ(Wt/L)ΔT, where Wt is the cross sectional areaof the membrane perpendicular to the direction of heat flow, and L isthe distance from the wire to the edge of the substrate. For a compositestructure, including the membrane plus a sample having thermalconductivity κ_(s), and thickness t_(s), power is given by therelationship P=(W/L)(κt+κ_(s)t_(s)) ΔT. ΔT can be determined from thewire's resistance, R=V/I=R_(o)(1+α(T−T_(o))), where R_(o) is theresistance at a reference temperature T_(o) and α is the temperaturecoefficient for the resistance. Thus, the power is linear in T and in R,and the slope is proportional to (κt+κ_(s)t_(s)).

This is a purely one-dimensional model, precisely valid only for aninfinitely long wire and membrane parallel to an infinite wafer edge.However, the sensor shown in FIG. 26 was designed to approximate thisgeometry in the region where the voltage and resistance are actuallybeing measured (between the two nodes on the membrane). This is truebecause the distance L from the wire to the edge of the membrane is muchshorter than the total width W of the membrane and the distance betweenthe nodes, and because the thermal conductance of the wire itself can beneglected (discussed below), so that almost all of the heat generated inthe wire passes through the membrane to the nearby wafer edge. Also, asshown below, the amount of energy lost to radiation is negligiblecompared to the amount conducted through the membrane.

In conducting the experiment, it was assumed that radiation could beneglected. The following calculation checks this assumption:

With no power applied to the wire, the entire sensor array and sensorare in thermal equilibrium with the environment at temperature T_(o), sothat there is no net emission or absorption of radiation by themembrane. When the wire is heated to a temperature T>T_(o), the netradiation emitted over the area where most of the heat flow is occurringis roughly given by P_(rad)=εσ(T⁴−T_(o) ⁴)(LW)≈4εσT_(o) ³ΔT(LW), whereΔT=T−T_(o) is the temperature rise of the wire, ε is the net emissivityof the membrane and sample, and σ=5.67×10⁻¹² watts/° K.⁴ cm² is theBoltzman radiation constant. Therefore the ratio of the amount of heatlost by radiation to that lost by conduction is given byβ=P_(rad)/P_(cond)=4εσT³L²/κt. For a good thermal conductivitymeasurement, β<<1 is required. For the sensor geometry shown in FIG. 26,L=10⁻² cm and t=0.4×10⁻⁵ cm Using the upper limit ε=1 for the emissivityand κ=0.15 Watts/cm° K. for silicon nitride, one obtains β≈0.01; so atmost 1% of the heat generated by the wire is lost to radiation.

Additionally, it may be shown that the heat which is conducted along thesensor wires to the wafer is small compared to the heat travelingthrough the membrane. The total thermal conductance of the membrane isapproximately 2.4×10⁻⁵ W/° K., while that of the wires is approximately4×10⁻⁷ W/° K. Although the thermal conductivity of Pt is about fivetimes higher than that of Si₃N₄, the heat conduction path through thewires is so much longer and narrower than that through the membrane thatthese losses may be ignored to a good approximation.

To test the thermal conductivity sensor, an aluminum film with athickness gradient was deposited on the back side of a 1×8 sensor array,using sputter coating from an A1 target. The thickness was controlled bymoving a computer-controlled shutter during deposition, yielding a filmthickness which ranged from 0 to 3500 Å in 500 Å steps.

There are many possible ways to resistively heat the wire whilemeasuring the resistance, in order to determine the thermalconductivity. One method is to make a series of DC current-voltagemeasurements, beginning with a power level which does not causesignificant self heating and increasing to higher values. From a plot ofP=IV versus R=V/I, the thermal conductance of the membrane and samplecan be determined. In order to take advantage of the low noise and highprecision which are easily attained using a lockin amplifier, however, asimilar method based on AC signals was used to analyze the test library.The electronics used to make the thermal conductivity measurement isshown in FIG. 27. A 1 kHz sinusoidal voltage V was used to drive avoltage-controlled current source, as shown in FIG. 27(a). (Note thatall voltages discussed here are RMS). The current passing through thesensor is given by V/360 Ω, where 360 Ω was the value of the seriesresistor in the current source circuit. Thus, a sinusoidal currentI=V/360 Ω was passed through the wire on the sensor membrane. A lockinamplifier was used to make a four-probe measurement of the voltage vacross the wire, between the two nodes on the membrane. Increasing theAC current amplitude increases the amount of DC self-heating, thetemperature, and the resistance (since the power has a DC component.Some of the detailed relationships between the different variables areshown in FIGS. 27B-D. Data for only three of the samples in the seriesare shown for clarity, with thicknesses of 50, 150, and 250 nm. FIG. 27Bshows the nonlinear current voltage characteristic, with the faster thanlinear rise due to self heating. The solid line is the theoretical I-Vcharacteristic for a 50 Ω resistance with no selfheating. The non-linearbehavior in the data becomes less pronounced as the A1 film becomesthicker, since heat is conducted away from the sensor more easily andless self heating occurs. FIG. 27C shows the resistance vs. the drivecurrent, showing the quadratic increase in resistance with current. Thelimiting value as I→0 is the resistance at ambient temperature. If therewas no self heating, the resistance would not change at all withincreasing current. Again, the resistance increase is more pronouncedfor thinner A1 films. FIG. 27D shows the power vs. resistance curve,illustrating the linear P vs. R behavior characteristic of heat loss bythermal conduction, as discussed above. For thicker A1 films, more poweris required to produce the same amount of temperature and resistanceincrease.

The software which controlled the measurements followed the followingsequence: a particular sensor in the array is connected to the currentsource and lockin by closing switches in the multiplexer and matrixswitch. An initial small value of I is sent to the sensor, chosen sothat the amount of self heating is negligible. The resulting voltage, v,across the wire is measured by the lockin and recorded by the computer52. The resistance of the wire is calculated in the same way as for a DCexperiment, R=v/I, P=Iv. The current amplitude I is then increased by afixed amount, and the measurements and calculations are repeated. Thedrive current is typically varied by a factor of 10 from the initial tothe final value in about 10 steps (corresponding to a factor of 100variation of the total power dissipated), and the lockin is allowed to“auto scale” as necessary to maintain the signal in range. At the end ofthis sequence of measurements, a plot of power vs. resistance isdisplayed, and a straight line is fit to this plot by the computer 52.The slope is proportional to the total thermal conductance of the sampleand membrane, and is stored by the computer. All of the raw data(voltages and currents) and calculated data (power and resistance) forthat sample are also stored. The multiplexer 126 then selects a newsensor, and the measurement is repeated.

FIG. 28 shows the best fit slope (in units of Watts per Ohm) as afunction of the film thickness. The thermal conductance increaseslinearly with the film thickness, again in agreement with the abovediscussions. In order to convert this number to an absolute value of thethermal conductivity of the sample material (A1), two additional stepsmust be taken. First, Watts/Ohm must be converted to Watts/° K (thermalconductance). This requires accurate knowledge of the temperaturecoefficient of the sensor wire's resistance, sincedP/dT=(dP/dR)*(dR/dT). Second, the thermal conductance must be convertedto thermal conductivity. This requires accurate knowledge of not onlythe film thickness, but also of all of the details of heat flow in thesensor structure, which will not be as simple as the one-dimensionalmodel described earlier and can only be obtained by detailed numericalmodeling of the sensor structure. Since dR/dT was not measured and theheat flows were not numerically modeled, a precise absolute analysis ofthe data is not possible at this time.

However, we can still use the data obtained to determine the ratio ofthe thermal conductivities K of silicon nitride and aluminum, and checkthis against the accepted values. The ratio of the thermal conductances,K, of two films, having different thicknesses, t, and thermalconductivities, K, but the same length, L, and width, W, is given byK₁/K₂=κ₁t₁/κ₂t₂. Solving for the thermal conductivity ratio for thisexperiment, using the data from FIG. 28 for the bare membrane (400 nmnitride only) and the thickest A1 sample (350 nm A1),κ_(A1)/κ_(Si3N4)=(K_(A1)/K_(Si3N4))(t_(Si3N4)/t_(A1))≈[(1.7×10⁻³ W/Ω)/(7.7×10⁻⁵ W/Ω)]*(350 nm/400 nm)≈19, where it has been assumed that thethermal conductivity in watts/° K will be proportional to the slopedP/dR in watts/Ω. It is known that the thermal conductivities of A1 andSi3N4 are 2.5 W/cm° K. and 0.1-0.15 W/cm° K. respectively, for a ratioof between 15:1 and 25:1. Thus, the measurements obtained are in fairagreement with accepted ratios of thermal conductivities.

It should be pointed out that it is probably possible to do thermalconductivity and heat capacity measurements on the same sensor. Forexample, although the heat capacity sensors are not optimized for use inthermal conductivity measurements, it has been observed that therelationship between power input, temperature, and thermal conductancestill holds at least qualitatively. There may be tradeoffs in optimizinga sensor for one function or the other, but it should be possible tocreate a design which is a good compromise.

Experimental Example: Magnetic Material Characterization

The sensor array of the present invention can also characterize themagnetic properties of materials libraries, again by changing possiblyonly the sensor structure in the sensor array and making minor changesin electronics and including equipment for generating a magnetic fieldas discussed with reference to transport properties. As explained above,the sensor array of the present invention can measure the Hallcoefficient of a material to determine the material's carrierconcentration and sign. In the present example, generally, an array ofunknown magnetic materials is placed on top of or in close proximity toan array of identically calibrated Hall effect sensors, which are madefrom a material with a known response to a magnetic field. An externalmagnetic field of variable strength is then imposed on the sample andsensor. The output of the Hall sensor is compared to the output of anidentical sensor that does not contain a sample. The difference in theresponse of the two sensors is due to the magnetization of the sample.In a preferred embodiment, the sensors with and without the sample areconnected in a differential arrangement, which greatly increases thesensitivity to the magnetization of the sample.

The samples may be deposited directly on a Hall sensor 210, as shown inFIG. 21A. In the illustrated structure, a sample 212 can be deposited onone portion 214 of the sensor, with a second portion 216 of the sensor210 left open to serve as a reference point. The difference between thevoltages V1 and V2 when the sensor 210 is placed in a magnetic fieldcorresponds to the magnetic properties of the sample 212. For example,the plot of the Hall voltage versus the magnetic field when there is nomaterial on the sensor will be a straight line, but a magnetic materialon the sensor 210 will cause the plot to deviate from the straight line,or will cause the straight line to have a different slope, because thesensor 210 is measuring both the external field and the field of thesample 212. In essence, the sensor 210 used in this embodiment is amagnetic field sensor. Alternatively, the Hall sensors and the samplesmay be contained on two separate substrates that are pressed togetherduring the measurement. This later method allows reuse of the Hallsensor array.

Another specific way in which the magnetic properties of a material canbe measured is by forming a sensor array containing cantilever sensors220, as shown in FIG. 21B. A material sample 222 is placed on arelatively soft, flexible cantilever 224, and then the sensor 220 isplaced in a magnetic field 226 having a known field strength and fieldgradient. The force and/or torque due to the interaction of the fieldand field gradient with the permanent and/or induced magnetization ofthe sample will cause the cantilever 224 to deflect. The amount of thedeflection will depend on the strength of the sample material's magneticcharacteristics.

There are several ways in which the deflection amount can be measuredprecisely. For example, the cantilever 224 on which the sample material222 is placed can be one half of a sandwich capacitor such that thecantilever deflection results in a capacitance change. An alternative isto place the cantilever 224 on a piezoresistor 228, which is shown inFIG. 21B, so that the bending of the cantilever 224 strains the resistorslightly, changing its resistance value. The electronic platform canthen monitor the amount the resistance changes and correlate the changewith the amount of deflection. Other methods of measuring the amount ofdeflection in the cantilever sensors 220 can be used without departingfrom the scope of the invention.

Detailed Discussion the Software Aspects of the Invention

The materials characterization system of the present invention uses acontrol processor, computer 52, to analyze the measurements and datagathered from the sensor array 10 for each material sample. In apreferred embodiment, the computer 52 is a personal computer, and willread and execute computer programs stored on any suitable computerreadable medium for use in automatically determining material propertiesfor materials associated with the sensor array 10.

The computer 52 includes an input device, for example, a keyboard,mouse, or other data inputting device, an output device, for example avisual display, an input/output adapter for uploading and downloadingdata and programming information from any suitable computer readablemedium, and a data input/output adapter for receiving and processingsignals emitted from the sensors 12. The computer 52 also includes amemory device, i.e., a computer readable medium. The memory devicestores the computer operating system for the computer 52 and anyadditional applications used by the computer 52. Those skilled in theart will appreciate that the memory device can comprise a random accessmemory and a read only memory formed as part thereof. Each of the abovedescribed components of the computer 52 communicate with one anotherthrough conventional means, for example a data bus bar.

The input/output adapter is equipped to receive data as well as computerprogramming instructions from any one, or combination of storage deviceswhich may include a magnetic floppy disk, a magnetic hard disk drive, amagnetic/digital tape, and/or a CD-ROM or any other suitable storagedevice. The data input/output adapter includes any necessary analog todigital, and digital to analog converts needed to process the datasignals received from the sensors 12.

The software comprising the computer program of the present inventionoperates on an operating system appropriate for the personal computer onwhich it is installed, such as Microsoft WindowsNT® operating system.The computer program can be stored as a file on a disk drive, CD-ROM orother computer readable storage medium as a series of files. Theoperating program loads the appropriate file and runs the executablecode contained in the file. In general, the control program of thepresent invention includes a series of program instructions, logic,designed to implement specific tasks. The computer program is dividedinto seven distinct tasks: (1) setting experimental conditions and testequipment operating parameters; (2) testing the sensor array; (3)measuring the raw data; (4) archiving the data; (5) reducing andarchiving the data; (6) viewing the results of the reduced data; and (7)retrieving data and re-reducing the data. It will be appreciated thatthe computer program may be readily adapted to complete tasks other thanthose identified.

1. Setting Experimental Conditions and Test Equipment Parameters

The computer program includes instructions for setting the experimentalconditions under which the sensor measurements are taken. For example,the operator can manually set the environment of the sensor array, e.g.,controlling variables such as temperature, pressure, atmosphericcomposition, etc., and calibrating the sensor array (discussed below).

2. Testing the Sensor Array

The software identifies the sensor array 10 by a unique identifier. Thisunique identifier may be used to retrieve the sensor array 10 for reviewor further analysis once the data gathering process has been completed.

The computer program also identifies and stores informationcharacterizing cells forming the sensor array 10 structure. In thedisclosed embodiment, the software identifies usable and unusable cellsof the sensor array 10. Usable cells are defined as those cells that arenot flagged as unusable, either automatically by the software ormanually by the user.

Information concerning usable and unusable cells can include thelocation of these cells in the sensor array 10, and these locations maybe stored on the computer 52 memory storage device. It will beappreciated that this information may be stored in other memory storagedevices. In the embodiment disclosed, the stored information is storedat a location and on a computer readable medium that is accessibly by adeposition software program that includes instructions for depositingthe material samples onto the sensor array 10.

The process for depositing the material samples onto the sensor array 10is not performed by the computer program of the present invention.However, the steps of depositing the material samples are summarizedherein to illustrate where they occur in the overall process. Thedeposition software and process includes the steps of (1) reading in amap of usable sensor array 10 cells; (2) mapping samples and calibrationstandards from the library to usable cells; and (3) writing thedeposition map to a database that includes explicit and editablesample-related parameters (such as hot tip temperature, platetemperature, and solvent type).

As part of the array testing instructions, the software can also includeinstructions for calibrating the sensors. In calibrating the sensors,materials having well-known material properties such as melting pointand glass transition temperatures are used as standards. In oneembodiment, materials such as high density polyethylene andethylene-butene are used as the material standards for calibrating thesensors. One of ordinary skill in the art will appreciate that thesematerials have well defined thermal properties. In calibrating thesensors, samples of the polyethylene and ethylene-butene materials areadded to the elements of the sensor array and measured to generatecorrections to the temperature calculation routine. This allows autocalibration of the sensor array 10 by finding the melting temperature ofthe standards and adjusting the sensor calibration to correct anyvariation.

Alternatively, the software may perform the function of calibrating thesensors to allow an accurate determination of the sample temperature.The temperature can be calculated from the sensor resistance but inorder for this to be done accurately, the relationship between theresistance and the temperature must be determined. For example, if thesensor resistance is linearly related to the temperature, it issufficient to measure the sensor resistance at two or more points anddetermine the change in resistance with temperature. This relationshipcan then be used to calculate the temperature for a given sensorresistance.

In one calibration method, one or more materials having well definedthermal transitions (such as glass transitions, melting points, orboiling points) at well known temperatures can be included within thelibrary as calibration standards. From a plot of the heat capacity ofthe standard material sample (in either absolute or unnormalized units)versus the sensor resistance, the resistance corresponding to thetransition of the material at the known transition temperature can bedetermined. Depending on the functional relationship between resistanceand temperature, and the degree of reproducibility of this relationshipfrom one sensor to the next, there will be some minimum number ofstandards that must be included in order to allow an accuratecalibration to be made. In some cases a single standard may besufficient, while in other cases two or more may be required.

In another calibration method, physical means are provided for heatingand/or cooling the entire sensor array to a series of knowntemperatures. At each temperature, the voltage from each sensor ismeasured and stored by the computer. From a series of such measurementsat several different temperatures, a calibration curve can beconstructed for each sensor.

3. Measuring the Raw Data

The computer program includes software instructions that identify thesensor array by a unique identifier; import the map of usable cells anddeposition library; set the operational parameters before executing theexperiment; run the calibration standards for the sensors; allow anoperator to select the usable cells in the sensor array 10 that are tobe tested; and run or execute the experiment, i.e., gathering data fromthe sensors 12 and performing the analysis thereof.

The general steps executed by the computer program in conducting theexperiment include:

(a) retesting the wafer (substrate) if necessary. If this step isperformed, all unusable cells will be flagged automatically;

(b) cooling the polymer products on the wafer using operator definedramp rates and set point temperatures over time;

(c) allowing a stable temperature to be reached; and

(d) measuring the material properties of the sample. For example,measuring the thermal properties of the samples such as the meltingtemperature (Tm) and glass transition temperature (Tg).

The software includes instructions permitting the operator to review theprocessed and raw data in real time. Conventional software instructionsand viewing apparatus are used in performing this task.

When the measured data includes the thermal properties of the materialsample, the thermal response data is analyzed to determine thetemperatures of the material sample such as the melting temperature (Tm)and glass transition temperature (Tg). For Tg, the temperature at halfheight of the step function in the thermal response (plotted on thehorizontal X-axis) is determined by an automated fitting routine. ForTm: The temperature (plotted on the horizontal X-axis) is determined bymeasuring the maximum of the melting peak in the sample thermalresponse.

A relative thermal response of the sample is calculated from the ratioof the measured first and third harmonic voltage. (This value as afunction of temperature is the data that will be stored.) For comparisonpurposes, the operator can autoscale the data so that the sampletemperature along the X-axis is the same in different plots.

Once the measurements have been completed, the operator may choose toeither store the wafer or wash and retest it, and then log the unusablecells. The operator may repeat the experiment any number of times usingdifferent operational parameters. For instance, the operator maymanually change the default operational parameters if necessary. Theoperator may also identify and flag any cells that to be excluded orskipped during the data gathering process, i.e., during the processingof receiving, monitoring and analyzing signals from the sensors 12.

5. Archiving the Data

The computer program software for performing this task includesinstructions for archiving both the raw and processed data usinggenerally known techniques. It will be appreciated by one of ordinaryskill in the art that the data is archived, stored, on a computerreadable medium.

6. Reducing the Data and Archiving the Reduced Data

The computer program software for performing this task includesinstructions for reducing and archiving both the raw and processed datausing generally known techniques. The data reduction function caninclude statistical analysis such as finding the minimum, maximum andmedian data points, or other analysis adapted for reducing the number ofdata points analyzed or reviewed.

The reduction process may be performed using conventional reductionsoftware programs such as Excel®, Kaleidagraph™ or similar softwareprograms. The computer program instructions for data reduction alsopermit the operator to select the reduced data to be stored on thememory device and to adjust this data manually.

The instructions for reducing the data also includes logic forautomatically archiving of the raw data, i.e., the compilation of andmeasurement of signals generated by the sensors 12, as well as theprocessed data.

It will be appreciated by one of ordinary skill in the art that programinstructions also include logic for archiving, storing, the data in theunreduced state. Generally known software instructions can be used toperform this task. Again, the data can be stored on a computer readablemedium of the type generally known and used in computer and dataprocessing systems, e.g., a CD-ROM, magnetic tape or magnetic disk.

7. Viewing the Results

Data may be viewed and analyzed using computer software package such asExcel®, Kaleidagraph™ or similar software programs. Information such asmelting point and glass transition temperatures can also be determinedvisually from a plot of heat capacity vs. temperature by observing thelocation of features in the plot.

Retrieving the Data and Reducing the Data

The computer program includes software instructions for retrieving thedata and reducing the data. This task is accomplished using reductionand archiving software instructions generally known in the field.

Description of the Software Program

The materials characterization system of the present invention iscomputer controlled and includes a software program for implementingmaterials characterization process previously described. In thedisclosed embodiment, the computer program is stored on a computerreadable medium containing software for the control of the operation ofan apparatus for characterizing one or more material properties for oneor more material samples. The software includes instructions forselecting a sensor or group of sensors for measurement, wherein eachsensor in the array is associated with a material sample; instructionsfor computing, selecting and setting of test equipment operatingparameters, wherein said instructions result in discrete operatingparameters used to drive the test equipment; instructions for initiatinga data gathering sequence, wherein the selected sensor or group ofsensors are caused to measure preselected material properties;instructions for sending, receiving and monitoring signals sent to andreceived from the selected sensor or group of sensors; instructions forprocessing signals received from the selected sensor or group ofsensors, wherein a specific output is generated for each signalprocessed; instructions for calculating an arithmetic valuecorresponding to a material property using the specific output generatedfor each signal processed; and instructions for monitoring and storingthe calculated arithmetic value, signals received during said datagathering sequence, and each specific output for each signal processed.

The computer program instructions for calculating an arithmetic valueinclude instructions for calculating the thermal properties of thematerial samples, wherein the instructions for calculating the thermalproperties include instructions for calculating at least one propertyselected from the group of melting point, glass transition temperature,heat capacity, thermal conductivity and thermal stability. The computeralso includes instructions for calculating at least one electricaltransport property selected from the group of electrical resistance,Hall coefficient, magnetoresistance, thermoelectric power, andcurrent-voltage characteristics. Further still, the computer programsoftware includes instructions for calculating at least one materialproperty from the group including viscosity, density, conductivity,molecular weight, chemical concentration, capacitance, dielectricconstant, mass loading, elasticity, damping, tensile strength, yieldstrength, ductility, toughness, hardness and magnetism. The computerprogram software also includes instructions for calculating the magneticproperties of the material samples. The computer software includesinstructions enabling the measurement of signals from two or moresensors on the same array.

The computer software further includes instructions for setting aruntime logic sequence for setting, limiting and monitoring the time forexecuting instructions for said data gathering sequence. The runtimelogic sequence enables a fixed time sequence to be set for completion ofthe experiment as discussed herein for heat capacity measurements.

The computer software further includes instructions for identifying thesensor array by a unique identifier. The computer software furtherincludes instructions for importing a map identifying the usable cellsof the sensor array. This information may be stored and viewed as thelocation(s) of usable cells within the sensor array, stored as databaseor another location that is accessible by a deposition software program.

The computer software further includes instructions for resetting a mapof the sensor array, wherein all unusable cells in the sensor array areidentified. The computer software includes instructions for selectivelyexcluding unusable cells from the data gathering sequence. For instance,the operator may select or exclude certain usable cells from inclusionin the data gathering sequence.

The computer software includes instructions for measuring the thermalproperties of a material sample associated with the selected sensor orgroup of sensors. Additionally, the computer software includesinstructions for calibrating the sensors.

Further still, the computer software includes instructions for cooling amaterial sample material supported on a substrate supporting the sensoryarray. The instructions for cooling the same include instructions forcontrolling the operational parameters of the test equipment such as theramp voltage, which may be selectively chosen by the operator.

Alternatively, the temperature of the samples may be controlled bycomputer program instructions enabling the control of the temperature ofthe selected sensor or group of sensors.

The computer software includes instructions for archiving, storing,retrieving and reducing the raw data (data obtained during the datagathering sequence), wherein the instructions for reducing include ananalysis algorithm. The computer software also includes instructions forarchiving, viewing retrieving and reducing the processed signal data, aswell as the calculated arithmetic value.

In an alternative embodiment, the computer program product is a computerreadable medium having computer program logic recorded thereon forenabling a processor in a computer system to analyze one or morematerial properties of a plurality of material samples, the computerprogram logic includes an inputting means for enabling a processor in acomputer to receive and process operator input; a selecting means forenabling the processor to drive a selected sensor or group of sensorsusing operator input received from the inputting means, wherein eachsensor forms a sensor array and each sensor of the sensor array isassociated with one or more materials samples; a driving means forenabling the processor to drive test equipment using operator inputreceived from the inputting means; an operating means for enabling theprocessor to execute a data gathering sequence, wherein preselectedproperties are measured by the selected sensor or group of sensors forone or more material samples associated the selected sensor or group ofsensors; a routing means for enabling communication between theoperating means and the selected sensor or group of sensors, processingmeans for enabling the processor to communicate with the operating meansin analyzing data signals received by the operating means; a determiningmeans for enabling the processor to determine an arithmetic valuerepresenting a preselected material property using signals received fromthe operating means; and a storing means for enabling the processor tostore data gathered during gathering sequence, data generated byprocessing means, or the arithmetic value.

One of ordinary skill in the art will appreciate that the computerprogram instructions used in controlling the material characterizationsystem of the present invention are of the type conventionally known andused in the industry. Additionally, one skilled in the art willappreciate that fact that the necessary algorithms for performing manyof the tasks and calculations required for the present invention aredisclosed throughout the specification or are commonly known and used inthe industry.

It should be understood that various alternatives to the embodiments ofthe invention described herein may be employed in practicing theinvention. It is intended that the following claims define the scope ofthe invention and that the methods and apparatus within the scope ofthese claims and their equivalents be covered thereby. The disclosuresof all articles and references, including patent applications andpublications, are incorporated herein by reference for all purposes.

What is claimed is:
 1. A computer readable medium containing softwarefor the control of the operation of an apparatus for characterizing oneor more material properties for a plurality of samples, the softwarecomprising: instructions for selecting an array of sensors formeasurement, each sensor of the array of sensors connected by a commonsubstrate, the array of sensors associated with a combinatorial array ofsamples, the array of samples being combinatorially synthesized suchthat each sample of the array of samples is at least slightly differentfrom other samples of the array of samples, each of the samples of thearray of samples associated with at least one sensor of the array ofsensors wherein the at least one sensor is different for each sample;instructions for computing, selecting and setting of test equipmentoperating parameters, wherein the instructions result in discreteoperating parameters used to drive the test equipment; instructions forinitiating a data gathering sequence, wherein the array of sensors arecaused to measure a preselected property for each of the samples of thearray of samples and wherein the preselected property is the same foreach of the samples of the array of samples; instructions for sending,receiving and monitoring signals sent to and received from the array ofsensors; instructions for processing signals received from the array ofsensors, wherein a specific output is generated for each signalprocessed; instructions for calculating arithmetic values correspondingto the preselected property of each of the samples of the array ofsamples using the specific output generated for each signal processed;instructions for monitoring and storing the calculated arithmetic value,the raw data, and each specific output for each signal processed; andinstructions for displaying the arithmetic value of each of the samplesof the array of samples together thereby allowing comparisons betweenthe preselected property of various samples of the array of samples. 2.The computer readable medium of claim 1, wherein the instructions forcalculating the arithmetic values include instructions for calculatingthe preselected property of the array of samples.
 3. The computerreadable medium of claim 2, wherein the preselected property is athermal material property selected from the group of melting point,glass transition temperature, heat capacity, thermal conductivity andthermal stability.
 4. The computer readable medium of claim 2, whereinthe preselected property is an electrical transport property selectedfrom the group of electrical resistance, Hall coefficient,magnetoresistance, thermoelectric power, and current-voltagecharacteristics.
 5. The computer readable medium of claim 2, wherein thepreselected property is selected from the group of viscosity, density,conductivity, molecular weight, chemical concentration, capacitance,dielectric constant, mass loading, elasticity, damping, tensilestrength, yield strength, ductility, toughness, hardness and magnetism.6. The computer readable medium of claim 2, wherein the preselectedproperty is a magnetic property.
 7. The computer readable medium ofclaim 1, wherein the software includes instructions for measuringsignals from two or more sensors on the same array.
 8. The computerreadable medium of claim 1, wherein the software further includesinstructions for setting a runtime logic sequence for setting, limitingand monitoring the time for executing instructions for the datagathering sequence.
 9. The computer readable medium of claim 1, whereinthe software further includes instructions for identifying the sensorarray by a unique identifier.
 10. The computer readable medium of claim1, wherein the software further includes instructions for importing amap identifying usable cells of the sensor array.
 11. The computerreadable medium of claim 10, wherein the instructions for importing amap identifying usable cells include instructions for identifying usablecells by location within the sensor array.
 12. The computer readablemedium of claim 10, wherein the instructions for importing a mapidentifying usable cells include instructions for storing the usablecell information in a database or a location that is accessible by adeposition software program.
 13. The computer readable medium of claim1, wherein the software further includes instructions for importing adeposition library supported by the sensor array.
 14. The computerreadable medium of claim 1, wherein the software further includesinstructions for resetting a map of the sensor array wherein allunusable cells in the sensor array are identified.
 15. The computerreadable medium of claim 1, wherein the software further includesinstructions for selectively excluding unusable cells from datagathering sequence.
 16. The computer readable medium of claim 1, whereinthe software further includes instructions for permitting the operatorto select or exclude certain usable cells from inclusion in the datagathering sequence.
 17. The computer readable medium of claim 1, whereinthe software further includes instructions for calibrating the sensors.18. The computer readable medium of claim 1, wherein the softwarefurther includes instructions for cooling a sample material supported ona substrate supporting the sensory array.
 19. The computer readablemedium of claim 18, wherein the instructions for cooling further includeinstructions for controlling the operational parameters of the testequipment.
 20. The computer readable medium of claim 1, wherein thesoftware further includes instructions for controlling the temperatureof the sensor array.
 21. The computer readable medium of claim 1,wherein the software further includes instructions for archiving the rawdata.
 22. The computer readable medium of claim 1, wherein the softwarefurther includes instructions for viewing the raw data.
 23. The computerreadable medium of claim 1, wherein the software further includesinstructions for retrieving the raw data.
 24. The computer readablemedium of claim 1, wherein the software further includes instructionsfor reducing the raw data.
 25. The computer readable medium of claim 24,wherein the instructions for reducing include an analysis algorithm. 26.The computer readable medium of claim 1, wherein the software furtherincludes instructions for archiving the processed signal data.
 27. Thecomputer readable medium of claim 1, wherein the software furtherincludes instructions for viewing the processed signal data.
 28. Thecomputer readable medium of claim 1, wherein the software furtherincludes instructions for retrieving the processed signal data.
 29. Thecomputer readable medium of claim 1, wherein the software furtherincludes instructions for reducing the processed signal data.
 30. Thecomputer readable medium of claim 1, wherein the software furtherincludes instructions for archiving the arithmetic values.
 31. Thecomputer readable medium of claim 1, wherein the software furtherincludes instructions for viewing the arithmetic values.
 32. Thecomputer readable medium of claim 1, wherein the software furtherincludes instructions for retrieving the arithmetic values.
 33. Thecomputer readable medium of claim 1, wherein the software furtherincludes instructions for reducing the data strings associated with thearithmetic values.
 34. The computer readable medium of claim 1, whereinthe software further includes instructions for storing the substrate orwashing or retesting the substrate and identifying the unusable cells.35. The computer readable medium of claim 1, wherein the computerreadable medium is a magnetic tape, magnetic disk, or compact disk. 36.A computer program product comprising a computer readable medium havingcomputer program logic recorded thereon for enabling a processor in acomputer system to analyze one or more material properties of aplurality of material samples, the computer program logic comprising:inputting means for enabling a processor in a computer to receive andprocess operator input; selecting means for enabling the processor todrive a selected sensor array using operator input received from theinputting means, each sensor of the array of sensors connected by acommon substrate, the array of sensors associated with a combinatorialarray of samples, the array of samples being combinatorially synthesizedsuch that each sample of the array of samples is at least slightlydifferent from other samples of the array of samples, each of thesamples of the array of samples associated with at least one sensor ofthe array of sensors wherein the at least one sensor is different foreach sample; driving means for enabling the processor to drive testequipment using operator input received from the inputting means;operating means for enabling the processor to execute a data gatheringsequence, wherein the array of sensors are caused to measure apreselected property for each of the samples of the array of samples andwherein the preselected property is the same for each of the samples ofthe array of samples; routing means for enabling communication betweenthe operating means and the array of sensors; processing means forenabling the processor to communicate with the operating means inanalyzing data signals received by the operating means; determiningmeans for enabling the processor to determine an arithmetic valuerepresenting the preselected property using signals received from theoperating means; and storing means for enabling the processor to storedata gathered during gathering sequence, data generated by processingmeans, or the arithmetic value; and display means for displaying thearithmetic value of each of the samples of the array of samples togetherthereby allowing comparisons between the preselected property of varioussamples of the array of samples.
 37. The computer readable medium ofclaim 36, wherein the computer program logic further includes viewingmeans for enabling the generation of a visual display of the datagathering sequence and data generated by processing means.
 38. Thecomputer readable medium of claim 36, wherein the computer program logicfurther includes viewing means for enabling the generation of a visualdisplay for viewing the data compiled during the data gathering sequenceand data generated by processing means.
 39. The computer readable mediumof claim 36, wherein the computer program logic further includes meansfor retrieving the data compiled during the data gathering sequence,data generated by processing means or the arithmetic values.
 40. Thecomputer readable medium of claim 36, wherein the computer program logicfurther includes means for reducing the data compiled during the datagathering sequence, data generated by processing means or the arithmeticvalues.
 41. The computer readable medium of claim 36, wherein thecomputer program logic further includes means for archiving the datacompiled during the data gathering sequence, data generated byprocessing means or the arithmetic values.
 42. The computer readablemedium of claim 36, wherein the determining means includes instructionsfor calculating the arithmetic values include instructions forcalculating the preselected property of the array of samples.
 43. Thecomputer readable medium of claim 42, wherein the preselected propertyis a thermal material property selected from the group of melting point,glass transition temperature, heat capacity, thermal conductivity andthermal stability.
 44. The computer readable medium of claim 42, whereinthe preselected property is an electrical transport property selectedfrom the group of electrical resistance, Hall coefficient,magnetoresistance, thermoelectric power, and current-voltagecharacteristics.
 45. The computer readable medium of claim 42, whereinthe preselected property is selected from the group of viscosity,density, conductivity, molecular weight, chemical concentration,capacitance, dielectric constant, mass loading, elasticity, damping,tensile strength, yield strength, ductility, toughness, hardness andmagnetism.
 46. The computer readable medium of claim 42, wherein thepreselected property is a magnetic property.
 47. The computer readablemedium of claim 36, wherein the determining means includes instructionsfor measuring signals from two or more sensors on the same array. 48.The computer readable medium of claim 36, wherein the computer programlogic further includes means for setting a runtime logic sequence forsetting, limiting and monitoring the time for executing instructions forthe data gathering sequence.
 49. The computer readable medium of claim36, wherein the computer program logic further includes means foridentifying the sensor array by a unique identifier.
 50. The computerreadable medium of claim 36, wherein the computer program logic furtherincludes means for importing a map identifying usable cells of thesensor array.
 51. The computer readable medium of claim 50, whereinmeans for importing a map identifying usable cells include instructionsfor identifying usable cells by location within the sensor array. 52.The computer readable medium of claim 50, wherein means for importing amap identifying usable cells include instructions for storing the usablecell information in a database or a location that is accessible by adeposition software program.
 53. The computer readable medium of claim36, wherein the computer program logic further includes means forimporting a deposition library supported by the sensor array.
 54. Thecomputer readable medium of claim 36, wherein the computer program logicfurther includes means for resetting a map of the sensor array whereinall unusable cells in the sensor array are identified.
 55. The computerreadable medium of claim 36, wherein the computer program logic furtherincludes means for excluding unusable cells from data gatheringsequence.
 56. The computer readable medium of claim 36, wherein computerprogram logic further includes means for permitting the operator toselect or exclude certain usable cells from inclusion in the datagathering sequence.
 57. The computer readable medium of claim 36,wherein the computer program logic further includes means forcalibrating the sensors.
 58. The computer readable medium of claim 36,wherein the computer program logic further includes means for cooling asample material supported on a substrate supporting the sensory array.59. The computer readable medium of claim 58, wherein means for coolingfurther includes instructions for controlling the operational parametersof the test equipment.
 60. The computer readable medium of claim 36,wherein the computer program logic further includes means forcontrolling the temperature of the array of sensors.
 61. The computerreadable medium of claim 36, wherein the computer readable medium is amagnetic tape, magnetic disk, or compact disk.